**8. Photodecomposition of bisphenol a (BPA)**

BPA is present in polycarbonate plastics and epoxy resins such as plastic water bottles, many food containers, water pipes, medical equipment, dental sealants, thermal receipts, electronics, and toys [10, 11]. The compound is toxic for the reproductive system because it mimics the human hormone estrogen. BPA production in the world exceeds 3 million tons per year. The BPA presence in the environment results in adverse effects on organic metabolism such as reproduction, metabolic systems, organism development, neural networks, and cardiovascular irrigation. The use of BPA is mostly as a plastic monomer, the monomer for epoxy, polycarbonate plastics, and epoxy resins. About all studied environment compartments have in some degree any content of BPA including air, water, and soil [9]. Published works indicate a connection between the BPA exposition and high levels of anxiety, depression, hyperactivity, and inattention. The BPA detection in organic body demonstrated its presence in blood, urine, cardiovascular diseases, diabetes, and obesity, posing a risk for fetal development and reducing the basal testosterone secretion. There is also a combination of BPA presence and other similar compounds in environmental compartments, food and food containers, and also in humans' milk, urine, and placental tissue; this is evidence of the possible global exposition.

The use of spiked sodium hypochlorite removes BPA from real water samples at 50 mg L<sup>−</sup><sup>1</sup> for 10 min with a removal percentage of 99%. In spite of the formation of chlorinated by-products during the process with some toxic side effects. The advanced UV/H2O2 was able to remove 85% of the initial BPA at 240 min. However, a high level of the H2O2 is essential to execute such BPA removal process. The presence of carbonates and bicarbonates reduces the UV/H2O2 efficiency due to scavenging radical's formation. The ozonation is an excellent option but is extremely costly and is suspected to form intermediates which carcinogenic nature [12].

The concentration = 20 mg L<sup>−</sup><sup>1</sup> , TiO2 dosage = 0.5 g L<sup>−</sup><sup>1</sup> , initial pH = 7.0, and temperature = 25°C followed the first-order model. The possible mechanisms for BPA photodegradation are in the following sequence:

1.Initial photooxidation, proceeded by electrophilic hydroxyl radicals (˙OH), produced the photocleavage of electron-rich carbons in the phenyl groups of BPA or the excited BPA molecules attacked by hydroxyl radicals (˙OH) forming phenol radicals (˙C6H4OH) and isopropylphenol radicals (˙C(CH3)2C6H4OH) [Eq. (6)].

**77**

*Green Water Treatment for Pharmaceutical Pollution DOI: http://dx.doi.org/10.5772/intechopen.85116*

4- hydroxyphenyl-2-propanol [Eq. (7)].

opening reactions results in aliphatic acids.

180 min in first-order kinetics with Kap = 20.3 10<sup>−</sup><sup>3</sup>

aliphatic acids [Eq. (8)].

concentration and 200 mg L<sup>−</sup><sup>1</sup>

in batch and stirrer tank.

than undoped TiO2.

HOC6H4C(CH3)2C6H4OH + (˙OH) → ˙C6H4OH + ˙C(CH3)2C6H4OH (6)

2.The hydroxyl radical (˙OH) converted to p-hydroquinone (HOC6H4OH) and isopropylphenol radical allow the formation of the 4-hydroxyphenyl intermediates such as p-hydroxybenzaldehyde, p-hydroxyacetophenone, and

HOCC6 H4OH or (HOC(CH3)C6H4OH or HOC(CH3)2C6H4OH) (7)

3.The oxidation reaction of the single-aromatic intermediates through ring-

The pH values decrease in aqueous media gradually, and the intermediates were entirely mineralized of forming carbon dioxide (CO2); the oxidization of the aromatic intermediates occurs subsequently through ring-opening reactions into

 Single − aromatic intermediates + ˙OH → aromatic ring opened products + ˙OH → CH3COOH + ˙OH → CO2 + H2O (8)

The UV-A radiation (λ = 365 nm) with TiO2 P25 result in complete removal after

eralization of BPA was at pH 3 after 120 min; intermediates formed at higher pH values are most stable and therefore difficult to be decomposed and mineralized [13, 14]. The TiO2 sources as anatase, rutile, brookite, and their mixtures indicate the lower uptakes with less than 6% were over the raw TiO2. The anatase and rutile TiO2 mixtures obtain 94 and 80% of removal percentage, respectively, higher than the obtained for the anatase, rutile, and brookite single composition. The mixture anatase/TiO2 brookite reached the complete mineralization, and the mixture of anatase and rutile was fivefold slower than the commercial TiO2 P25 with 3 min of complete removal percentage. All products showed less toxicity and estrogenic activity than the initial BPA [15, 16]. The nano-TiO2 facilitates the degradation under sunlight radiation with O2

dominant oxidizing species. The better degradation efficiency was at pH 2.6, and correspondent with the pseudo-first-order without nanoparticles was one or two

The higher results were with anatase particles enhanced by the presence of rutile and preferential oxidation of reaction intermediates on brookite. The toxicity removal was for TiO2 supported on a glass fiber with UV light radiation λ = 365 nm

The use of a wide range of metals as the lanthanum-doped TiO2 was able to degrade BPA completely under acidic conditions within 2 h; the result is far better

The oxidants' addition enhances efficiency, as H2O2 and FeII. The H2O2 interacted with Fe-2þ ions to produce hydroxyl radicals. The Fe doped into the TiO2 decreased the bandgap, which also enhanced the BPA photodegradation. The addition of 5 mol% of Fe in TiO2 successfully removed 10 ppm of BPA in 2 h. The experiment with nitrogen doping on TiO2 indicated the N-doped TiO2 enhanced the photodegradation of BPA compared to conventional TiO2. Likewise, the iodinedoped TiO2, upon exposure to UV and visible irradiation, showed increased degra-

orders small with λ = 365 nm of radiation using pristine nanotubes [10].

dation efficiencies for BPA up to 93 and 100%, respectively.

min<sup>−</sup><sup>1</sup>

as the addition of the TiO2 P25 [3]. The complete min-

, with 5 mgL<sup>−</sup><sup>1</sup>

as initial

−2 as

˙C6H4OH + ˙OH → HOC6H4OH + ˙C(CH3)2C6H4OH + ˙OH →

*Green Chemistry Applications*

possible global exposition.

The concentration = 20 mg L<sup>−</sup><sup>1</sup>

50 mg L<sup>−</sup><sup>1</sup>

0.38 h<sup>−</sup><sup>1</sup>

significant crystallization of anatase.

applications; at the lowest calcination temperature tested (300°C), there is no

these materials, acting as trap centers or the photogenerated charges.

in acetaminophen photodegradation. Some references mentioned the O2

**8. Photodecomposition of bisphenol a (BPA)**

Published results indicated the pseudo-first-order rates were 0.13, 0.19, and

 for complete photodecomposition of antipyrine, acetaminophen, and ibuprofen, respectively. Regarding with the properties of the C-TiO2 semiconductor materials, the structured defects caused by the C incorporation (as substitutional anion or interstitial cation) are the responsible for the photocatalytic activity of

The investigation of the role of the reactive oxygen species used selected scavengers as isopropanol, the OH radical scavenger; the addition reduced the degradation rate. The OH radicals are very reactive, and the reduction by the scavenger inhibited the degradation rate, an indication of the involvement of the OH radical production

attack preferentially organic compounds with aromatic rings (as ACE aromatic ring).

BPA is present in polycarbonate plastics and epoxy resins such as plastic water

The use of spiked sodium hypochlorite removes BPA from real water samples at

of chlorinated by-products during the process with some toxic side effects. The advanced UV/H2O2 was able to remove 85% of the initial BPA at 240 min. However, a high level of the H2O2 is essential to execute such BPA removal process. The presence of carbonates and bicarbonates reduces the UV/H2O2 efficiency due to scavenging radical's formation. The ozonation is an excellent option but is extremely costly and is

temperature = 25°C followed the first-order model. The possible mechanisms for

1.Initial photooxidation, proceeded by electrophilic hydroxyl radicals (˙OH), produced the photocleavage of electron-rich carbons in the phenyl groups of BPA or the excited BPA molecules attacked by hydroxyl radicals (˙OH) forming phenol radicals (˙C6H4OH) and isopropylphenol radicals (˙C(CH3)2C6H4OH)

suspected to form intermediates which carcinogenic nature [12].

BPA photodegradation are in the following sequence:

for 10 min with a removal percentage of 99%. In spite of the formation

, TiO2 dosage = 0.5 g L<sup>−</sup><sup>1</sup>

, initial pH = 7.0, and

bottles, many food containers, water pipes, medical equipment, dental sealants, thermal receipts, electronics, and toys [10, 11]. The compound is toxic for the reproductive system because it mimics the human hormone estrogen. BPA production in the world exceeds 3 million tons per year. The BPA presence in the environment results in adverse effects on organic metabolism such as reproduction, metabolic systems, organism development, neural networks, and cardiovascular irrigation. The use of BPA is mostly as a plastic monomer, the monomer for epoxy, polycarbonate plastics, and epoxy resins. About all studied environment compartments have in some degree any content of BPA including air, water, and soil [9]. Published works indicate a connection between the BPA exposition and high levels of anxiety, depression, hyperactivity, and inattention. The BPA detection in organic body demonstrated its presence in blood, urine, cardiovascular diseases, diabetes, and obesity, posing a risk for fetal development and reducing the basal testosterone secretion. There is also a combination of BPA presence and other similar compounds in environmental compartments, food and food containers, and also in humans' milk, urine, and placental tissue; this is evidence of the

<sup>−</sup> radicals

**76**

[Eq. (6)].

HOC6H4C(CH3)2C6H4OH + (˙OH) → ˙C6H4OH + ˙C(CH3)2C6H4OH (6)

2.The hydroxyl radical (˙OH) converted to p-hydroquinone (HOC6H4OH) and isopropylphenol radical allow the formation of the 4-hydroxyphenyl intermediates such as p-hydroxybenzaldehyde, p-hydroxyacetophenone, and 4- hydroxyphenyl-2-propanol [Eq. (7)].

 ˙C6H4OH + ˙OH → HOC6H4OH + ˙C(CH3)2C6H4OH + ˙OH → HOCC6 H4OH or (HOC(CH3)C6H4OH or HOC(CH3)2C6H4OH) (7)

3.The oxidation reaction of the single-aromatic intermediates through ringopening reactions results in aliphatic acids.

The pH values decrease in aqueous media gradually, and the intermediates were entirely mineralized of forming carbon dioxide (CO2); the oxidization of the aromatic intermediates occurs subsequently through ring-opening reactions into aliphatic acids [Eq. (8)].

 Single − aromatic intermediates + ˙OH → aromatic ring opened products + ˙OH → CH3COOH + ˙OH → CO2 + H2O (8)

The UV-A radiation (λ = 365 nm) with TiO2 P25 result in complete removal after 180 min in first-order kinetics with Kap = 20.3 10<sup>−</sup><sup>3</sup> min<sup>−</sup><sup>1</sup> , with 5 mgL<sup>−</sup><sup>1</sup> as initial concentration and 200 mg L<sup>−</sup><sup>1</sup> as the addition of the TiO2 P25 [3]. The complete mineralization of BPA was at pH 3 after 120 min; intermediates formed at higher pH values are most stable and therefore difficult to be decomposed and mineralized [13, 14]. The TiO2 sources as anatase, rutile, brookite, and their mixtures indicate the lower uptakes with less than 6% were over the raw TiO2. The anatase and rutile TiO2 mixtures obtain 94 and 80% of removal percentage, respectively, higher than the obtained for the anatase, rutile, and brookite single composition. The mixture anatase/TiO2 brookite reached the complete mineralization, and the mixture of anatase and rutile was fivefold slower than the commercial TiO2 P25 with 3 min of complete removal percentage. All products showed less toxicity and estrogenic activity than the initial BPA [15, 16].

The nano-TiO2 facilitates the degradation under sunlight radiation with O2 −2 as dominant oxidizing species. The better degradation efficiency was at pH 2.6, and correspondent with the pseudo-first-order without nanoparticles was one or two orders small with λ = 365 nm of radiation using pristine nanotubes [10].

The higher results were with anatase particles enhanced by the presence of rutile and preferential oxidation of reaction intermediates on brookite. The toxicity removal was for TiO2 supported on a glass fiber with UV light radiation λ = 365 nm in batch and stirrer tank.

The use of a wide range of metals as the lanthanum-doped TiO2 was able to degrade BPA completely under acidic conditions within 2 h; the result is far better than undoped TiO2.

The oxidants' addition enhances efficiency, as H2O2 and FeII. The H2O2 interacted with Fe-2þ ions to produce hydroxyl radicals. The Fe doped into the TiO2 decreased the bandgap, which also enhanced the BPA photodegradation. The addition of 5 mol% of Fe in TiO2 successfully removed 10 ppm of BPA in 2 h. The experiment with nitrogen doping on TiO2 indicated the N-doped TiO2 enhanced the photodegradation of BPA compared to conventional TiO2. Likewise, the iodinedoped TiO2, upon exposure to UV and visible irradiation, showed increased degradation efficiencies for BPA up to 93 and 100%, respectively.

The 4-chlorophenol, phenol, methylene blue, rhodamine B, and acid orange presence reduces the surface area for the volume and enhances the oxygen vacancies in TiO2 surface matrix by N-doping and F-doping, and surface acidity is also improved by F-doping, and visible light adsorption by N-doping of nitrogenfluorine-codoped TiO2 photocatalyst. The use of simulated sunlight lamps promotes the generation of the active species for BPA decomposition as O2 −2 .

The production of TiO2 PEG started with the mixture of titanium ethoxide and ethanol solution followed by PEG addition; the suspension aged for 24 h and calcined for 2 h at 400°C. The optimization of the TiO2 production by sol–gel polyethylene glycol (PEG) includes the variation of the PEG molecular weight, the mass percentage, the pH, and the TiO2 dose. The visible light BPA degradation rates for TiO2 with PEG200 (10%), PEG600 (5%), and PEG3500 (0.5%) at pH 4 were 2.07, 3.01, and 2.90 h<sup>−</sup><sup>1</sup> , respectively. After 12 h of reaction, the total organic carbon measurements indicated a small BPA degradation with the reduction of TiO2, with PEG200 (10%), PEG600 (5%), and PEG3500 (0.5%) of 38%, 56%, 65%, and 64%, respectively. The content of hydroxyl radicals in TiO2, with PEG200 (10%), PEG600 (5%), and PEG3500 (0.5%), was 50.1, 88.6, 78.8, and 75.1 μM, respectively. Allowing the conclusion about the PEG addition on the TiO2 preparation increases the photoactivity, and the optimal PEG addition percentage varied with PEG molecular weight and content.

## **9. Antibiotic photodecomposition**

The antibiotic removal and other anthropogenic compounds by adsorption are the major chemical process of deactivation, and it is important to reduce the toxic properties and to restrict their transport into water systems. The adsorbent material in combination with titanium dioxide or titania (Ti) showed better results using adsorption combined with photocatalytic activity with low cost, nontoxicity, and high stability in aqueous solution. Nevertheless, the disadvantages of TiO2 powders are the low surface area (Degussa P25 = 35–45 m2 g<sup>−</sup><sup>1</sup> , anatase < m2 g<sup>−</sup><sup>1</sup> ); the anatase bandgap of 3.20 eV uses only a small UV fraction of solar light, about 2–3%, with the high cost of the TiO2 powder separation and recovery from treated wastewater [17, 18].

The removal of tetracycline (TC) by TiO2 and the mesoporous binary system TiO2-SiO2 was tested, and it is strongly dependent on pH, with increasing pH it decreases. The electrostatic forces and H-bond formations mainly between amide, carboxylic, and phenolic groups of the antibiotic and the functional groups of TiO2 are also important. The adsorption capacity increases in the following order TiO2 < TiO2-SiO2 (high surface area). The photodegradation rate is affected by pH 7 or lower; the related mechanism is to OH˙ radicals—the composed titania-silica act as an adsorbent and alternative photocatalyst for pollution control.

All processes result in high degradation efficiency of the β-lactam antibiotic (oxacillin). The TiO2 photocatalysis, the sonochemistry, the photo-Fenton process, and electrochemistry (with a Ti/IrO2 anode in sodium chloride solution). The processes are successful ,but three of them involve the hydroxyl radical generation and the degradation pathways, by-products' generation, and the mineralization degree. The electrochemical process performed the decomposition by chlorine production and its attack when the sonochemical and photo-Fenton systems have the production of the hydroxyl radical.

The high oxidant species with low selectivities, such as hydroxyl radicals (E = 2.8 V), are formed in advanced oxidation processes (AOPs) and the active chlorine electrogenerated through dimensionally stable anodes (DSA). The irradiation of an aqueous suspension of TiO2-semiconductor with UV light produces hydroxyl radical.

**79**

*Green Water Treatment for Pharmaceutical Pollution DOI: http://dx.doi.org/10.5772/intechopen.85116*

HClO,CLO<sup>−</sup>

e

hydroxyl radicals.

TiO2 + hν (λ < 387 nm) → TiO2 (e

<sup>−</sup> + O2 → ˙O<sup>−</sup>

electrochemical treatments, the pollutant was not mineralized.

hydroxyl radicals in a photo-Fenton process.

The TiO2 photocatalysis combines the holes' generation with the attack of the hydroxyl radicals. The by-product analysis indicated the four oxidation processes exhibited the oxidation of the thioether radical followed by the amide breakdown and finally the β-lactam opening ring. However, the antibiotic decarboxylation was only a result of the TiO2 photocatalysis, explained by the holes' production with direct oxacillin oxidation [Eqs. (9)–(15)]. The electrochemical process promotes the oxacillin isomerization pathway, while the photo-Fenton and TiO2 photocatalysis treatments showed hydroxylation at the aromatic ring. The different degradation

P + ˙OH → Pox (9)

h<sup>+</sup> + H2O → H<sup>+</sup> + ˙OH (12)

h<sup>+</sup> + OH<sup>−</sup> → ˙OH (13)

h<sup>+</sup> + P → Pox (14)

The total organic carbon measurements in TiO2 photocatalysis and the photo-Fenton system were 90 and 35%, respectively, and with just the sonochemical and

The presence of the ultrasonic waves in aqueous solutions is another way to form hydroxyl radicals [Eqs. (16)–(19)]. Singular conditions of temperature (5000 K) and pressure (1000 atm) induce the formation of ultrasonic microbubbles which violently collapse in water, and the dissolved oxygen is dissociated to produce

H2O + ))) → ˙H + ˙OH (16)

O2 + ))) → 2˙O (17)

H2O + ˙O → 2˙OH (18)

O2 + ˙H → ˙O + ˙OH (19)

The reaction of Fe (II) with hydrogen peroxide produces radicals. The reduction of Fe (III) in aqueous media results in Fe (II) by the action of UV–Vis light and extra

The electrochemical oxidation which soluble chloride results in chloride anions on the Ti/IrO2 anode [Eq. (20)] which the generation of hypochlorous and hydrochloric acids [Eq. (21)]. The dissociation of the hypochlorous acid forms

,Cl2 + P → Pox (10)

) (11)

<sup>−</sup> + h<sup>+</sup>

<sup>2</sup> → → ˙OH, ˙OOH,H2O2 (15)

routes generated different mineralization extent and efficiency [19].

*Green Water Treatment for Pharmaceutical Pollution DOI: http://dx.doi.org/10.5772/intechopen.85116*

*Green Chemistry Applications*

**9. Antibiotic photodecomposition**

area (Degussa P25 = 35–45 m2

tion of the hydroxyl radical.

hydroxyl radical.

2.90 h<sup>−</sup><sup>1</sup>

The 4-chlorophenol, phenol, methylene blue, rhodamine B, and acid orange presence reduces the surface area for the volume and enhances the oxygen vacancies in TiO2 surface matrix by N-doping and F-doping, and surface acidity is also improved by F-doping, and visible light adsorption by N-doping of nitrogen-

fluorine-codoped TiO2 photocatalyst. The use of simulated sunlight lamps promotes

The production of TiO2 PEG started with the mixture of titanium ethoxide and ethanol solution followed by PEG addition; the suspension aged for 24 h and calcined for 2 h at 400°C. The optimization of the TiO2 production by sol–gel polyethylene glycol (PEG) includes the variation of the PEG molecular weight, the mass percentage, the pH, and the TiO2 dose. The visible light BPA degradation rates for TiO2 with PEG200 (10%), PEG600 (5%), and PEG3500 (0.5%) at pH 4 were 2.07, 3.01, and

, respectively. After 12 h of reaction, the total organic carbon measurements

The antibiotic removal and other anthropogenic compounds by adsorption are the major chemical process of deactivation, and it is important to reduce the toxic properties and to restrict their transport into water systems. The adsorbent material in combination with titanium dioxide or titania (Ti) showed better results using adsorption combined with photocatalytic activity with low cost, nontoxicity, and high stability in aqueous solution. Nevertheless, the disadvantages of TiO2 powders are the low surface

g<sup>−</sup><sup>1</sup>

, anatase < m2

uses only a small UV fraction of solar light, about 2–3%, with the high cost of the TiO2

The removal of tetracycline (TC) by TiO2 and the mesoporous binary system TiO2-SiO2 was tested, and it is strongly dependent on pH, with increasing pH it decreases. The electrostatic forces and H-bond formations mainly between amide, carboxylic, and phenolic groups of the antibiotic and the functional groups of TiO2 are also important. The adsorption capacity increases in the following order TiO2 < TiO2-SiO2 (high surface area). The photodegradation rate is affected by pH 7 or lower; the related mechanism is to OH˙ radicals—the composed titania-silica act

All processes result in high degradation efficiency of the β-lactam antibiotic (oxacillin). The TiO2 photocatalysis, the sonochemistry, the photo-Fenton process, and electrochemistry (with a Ti/IrO2 anode in sodium chloride solution). The processes are successful ,but three of them involve the hydroxyl radical generation and the degradation pathways, by-products' generation, and the mineralization degree. The electrochemical process performed the decomposition by chlorine production and its attack when the sonochemical and photo-Fenton systems have the produc-

The high oxidant species with low selectivities, such as hydroxyl radicals (E = 2.8 V), are formed in advanced oxidation processes (AOPs) and the active chlorine electrogenerated through dimensionally stable anodes (DSA). The irradiation of an aqueous suspension of TiO2-semiconductor with UV light produces

indicated a small BPA degradation with the reduction of TiO2, with PEG200 (10%), PEG600 (5%), and PEG3500 (0.5%) of 38%, 56%, 65%, and 64%, respectively. The content of hydroxyl radicals in TiO2, with PEG200 (10%), PEG600 (5%), and PEG3500 (0.5%), was 50.1, 88.6, 78.8, and 75.1 μM, respectively. Allowing the conclusion about the PEG addition on the TiO2 preparation increases the photoactivity, and the optimal PEG addition percentage varied with PEG molecular weight and content.

−2 .

); the anatase bandgap of 3.20 eV

the generation of the active species for BPA decomposition as O2

g<sup>−</sup><sup>1</sup>

powder separation and recovery from treated wastewater [17, 18].

as an adsorbent and alternative photocatalyst for pollution control.

**78**

The TiO2 photocatalysis combines the holes' generation with the attack of the hydroxyl radicals. The by-product analysis indicated the four oxidation processes exhibited the oxidation of the thioether radical followed by the amide breakdown and finally the β-lactam opening ring. However, the antibiotic decarboxylation was only a result of the TiO2 photocatalysis, explained by the holes' production with direct oxacillin oxidation [Eqs. (9)–(15)]. The electrochemical process promotes the oxacillin isomerization pathway, while the photo-Fenton and TiO2 photocatalysis treatments showed hydroxylation at the aromatic ring. The different degradation routes generated different mineralization extent and efficiency [19].

$$\text{P} + \text{'OH} \rightarrow \text{Pox} \tag{9}$$

$$\text{HClO}, \text{CLO}^{-}, \text{Cl}\_{2} + \text{P} \to \text{Pox} \tag{10}$$

$$\text{TiO}\_2 \star \text{h}\nu \text{ ( $\lambda$ } < \text{387 nm)} \rightarrow \text{TiO}\_2 \text{ (e}^- \star \text{h}^+ \text{)}\tag{11}$$

$$\text{H}^+ + \text{H}\_2\text{O} \rightarrow \text{H}^+ + \text{'OH} \tag{12}$$

$$\text{h}^\* \star \text{OH}^- \rightarrow \text{'OH} \tag{13}$$

$$\text{h}^\* + \text{P} \to \text{P}\_{\text{ox}} \tag{14}$$

$$\text{e}^- + \text{O}\_2 \rightarrow \text{'O}^- \rightarrow \rightarrow \text{'OH,'} \\ \text{'OOH,H}\_2\text{O}\_2 \tag{15}$$

The total organic carbon measurements in TiO2 photocatalysis and the photo-Fenton system were 90 and 35%, respectively, and with just the sonochemical and electrochemical treatments, the pollutant was not mineralized.

The presence of the ultrasonic waves in aqueous solutions is another way to form hydroxyl radicals [Eqs. (16)–(19)]. Singular conditions of temperature (5000 K) and pressure (1000 atm) induce the formation of ultrasonic microbubbles which violently collapse in water, and the dissolved oxygen is dissociated to produce hydroxyl radicals.

H2O + ))) → ˙H + ˙OH (16)

$$\left|\bullet\right|\_{2}\leftrightarrow\left|\bullet\right|\qquad\qquad\qquad\qquad\qquad\qquad\qquad\qquad\qquad\qquad\bullet\qquad\bullet$$

$$\text{H}\_2\text{O} + \text{'O} \rightarrow \text{2'}\text{OH} \tag{18}$$

$$\text{O}\_2 \text{ + 'H} \rightarrow \text{'O} \text{ + 'OH} \tag{19}$$

The reaction of Fe (II) with hydrogen peroxide produces radicals. The reduction of Fe (III) in aqueous media results in Fe (II) by the action of UV–Vis light and extra hydroxyl radicals in a photo-Fenton process.

The electrochemical oxidation which soluble chloride results in chloride anions on the Ti/IrO2 anode [Eq. (20)] which the generation of hypochlorous and hydrochloric acids [Eq. (21)]. The dissociation of the hypochlorous acid forms

hypochlorite [Eq. (22)]. Chlorine, hypochlorous acid, and hypochlorite are active species, and they are very dependent on the pH values. The predominant species at pH lower than 3 is Cl2 (E = 1.36 V), in the range of pH 3 to 8 is HClO<sup>−</sup> (E = 1.49 V), and at pH higher than 8 is OCl<sup>−</sup> (E = 0.89 V).

$$\text{2Cl}^- \rightarrow \text{Cl}\_2 + \text{2e}^- \tag{20}$$

$$\text{Cl}\_2 + \text{H}\_2\text{O} \rightarrow \text{HClO} + \text{HCl} \tag{21}$$

$$\text{HClO}^{-} + \text{H}\_{2}\text{O} \rightarrow \text{ClO}^{-} + \text{H}\_{3}\text{O}^{+} \tag{22}$$

The knowledge of the oxidation routes in water treatment can optimize the process and establish a pollutant degradation mechanism and pathways: the experimental parameters and the matrix influence on oxacillin (OXA) on electrochemical oxidation and TiO2 photocatalysis. Here is no report about photo-Fenton and sonochemical processes' removal of oxacillin from polluted water.

The sonochemical process degraded the antibiotic and generates solutions without OXA entirely; the antimicrobial activity showed an excellent performance and adjustment to exponential kinetic-type decay, and the degradation rates were 1.4 μM min<sup>−</sup><sup>1</sup> for OXA, 1.3 μM min<sup>−</sup><sup>1</sup> for OXA with mannitol, and 1.4 μM min<sup>−</sup><sup>1</sup> for OXA with calcium carbonate. The possible OXA sonic degradation mechanism was proposed based on the evolution of the by-products and their chemical structure [Eqs. (16) and (17)] [20].

The ultrasound application over 120 min removed OXA compounds and eliminated its antimicrobial activity. However, the mineralization was not reached even after (360 min). The mineralization of the oxacillin under previous water sonication reduce the microbial activity even with non-adapted microorganisms from a municipal wastewater treatment plant. The results showed the sonochemical transformation of the initial pollutant into biotreatable substances even using the typical aerobic biological system.

The iron ions present in the matrix affect the antibiotic (OXA) decomposition, with improvement in degradation, and the inhibition was by the addition of pharmaceutical excipients of a commercial formulation or by inorganic ions of natural mineral water. The best performances were achieved at natural pH 6.0 using 2.0 g L<sup>−</sup><sup>1</sup> of TiO2 with 150 W of light intensity. The OXA photodegradation process showed a Langmuir-Hinshelwood kinetic model. The achievement of the total antibiotic removal was after 120 min, with 100% of mineralization. Finally, the identification of five by-products elucidates the degradation routes with a proposition of an antibiotic degradation (**Figure 2**).

The addition of 2-propanol as a scavenger, 25 times higher than the antibiotic, produces a slight reduction (about 3%) in the antibiotic removal rate, and the concentration of 645 times higher than the OXA causes 30% of inhibition. The result indicates the hydroxyl radicals present at the solution may contribute to the degradation of the antibiotic molecules. The essays in the presence of KI concentration 25 times higher than the OXA concentration showed 75% of inhibition. The use of equimolar KI concentration resulted in a 13% reduction. The indication of the degradation rate is in association with adsorption reduction of the catalyst surface. Consequently, the degradation of OXA by heterogeneous photocatalysis seems to occur mostly at the catalyst surface and via two routes: by the radical attack and photo-Kolbe mechanism.

The UV irradiation of antibiotic molecules generates excited states and the detection of such reactive species by an indication of their ability to oxidize luminal reagent. Such compound uses the electronically excited aminophthalate, which

**81**

*Green Water Treatment for Pharmaceutical Pollution DOI: http://dx.doi.org/10.5772/intechopen.85116*

decays to the ground state releasing electromagnetic radiation in the visible zone of the spectrum—the application of the method to penicillin G, nafcillin, azlocillin, and neomycin dissolved in water. The intensity of the luminal chemiluminescence emission (CL) was proportional to the radical concentration and dependent on the molecular structure of the drugs. Under the optimized conditions, the penicillin and azlocillin were the most susceptible to photodegradation, while neomycin sulfate was less affected by the UV light. The addition of a hydroalcoholic extract of rose petals to antibiotic solutions reduced the CL intensity, indicating the alcohol

In the application of the solar photodecomposition in the dye mixture of RH and MB, the result is similar with a single dye, and the adsorption balance remains unchanged with no interaction between RH and MB and their by-products. Nevertheless, the addition of MO in the mixture accelerated the photodecomposition significantly. The decomposition of RH/MO and the MB/MO reduced the decomposition time in 13 and 10 min, respectively [21]. Such an effect is positively dependent on the MO concentration; the application of Eq. (23) to the Langmuir-

where Co and C are the initial and t measured concentrations, t is the reaction time, and k are the first-order-kinetic reaction constant, calculated using

Kt = kt (23)

act as a scavenger of free radicals of the irradiated drugs.

−ln(C/Co) = k'

**10. Synergistic effect**

*Oxacillin photodegradation pathway.*

**Figure 2.**

Hinshelwood model

log(C/Co) vs. t.

*Green Water Treatment for Pharmaceutical Pollution DOI: http://dx.doi.org/10.5772/intechopen.85116*

*Green Chemistry Applications*

1.4 μM min<sup>−</sup><sup>1</sup>

2.0 g L<sup>−</sup><sup>1</sup>

[Eqs. (16) and (17)] [20].

typical aerobic biological system.

tion of an antibiotic degradation (**Figure 2**).

and at pH higher than 8 is OCl<sup>−</sup> (E = 0.89 V).

hypochlorite [Eq. (22)]. Chlorine, hypochlorous acid, and hypochlorite are active species, and they are very dependent on the pH values. The predominant species at pH lower than 3 is Cl2 (E = 1.36 V), in the range of pH 3 to 8 is HClO<sup>−</sup> (E = 1.49 V),

2Cl<sup>−</sup> → Cl2 + 2e<sup>−</sup> (20)

Cl2 + H2O → HClO + HCl (21)

HClO<sup>−</sup> + H2O → ClO<sup>−</sup> + H3O<sup>+</sup> (22)

The knowledge of the oxidation routes in water treatment can optimize the process and establish a pollutant degradation mechanism and pathways: the experimental parameters and the matrix influence on oxacillin (OXA) on electrochemical oxidation and TiO2 photocatalysis. Here is no report about photo-Fenton and

The sonochemical process degraded the antibiotic and generates solutions without OXA entirely; the antimicrobial activity showed an excellent performance and adjustment to exponential kinetic-type decay, and the degradation rates were

OXA with calcium carbonate. The possible OXA sonic degradation mechanism was proposed based on the evolution of the by-products and their chemical structure

The ultrasound application over 120 min removed OXA compounds and eliminated its antimicrobial activity. However, the mineralization was not reached even after (360 min). The mineralization of the oxacillin under previous water sonication reduce the microbial activity even with non-adapted microorganisms from a municipal wastewater treatment plant. The results showed the sonochemical transformation of the initial pollutant into biotreatable substances even using the

The iron ions present in the matrix affect the antibiotic (OXA) decomposition, with improvement in degradation, and the inhibition was by the addition of pharmaceutical excipients of a commercial formulation or by inorganic ions of natural mineral water. The best performances were achieved at natural pH 6.0 using

showed a Langmuir-Hinshelwood kinetic model. The achievement of the total antibiotic removal was after 120 min, with 100% of mineralization. Finally, the identification of five by-products elucidates the degradation routes with a proposi-

of TiO2 with 150 W of light intensity. The OXA photodegradation process

The addition of 2-propanol as a scavenger, 25 times higher than the antibiotic, produces a slight reduction (about 3%) in the antibiotic removal rate, and the concentration of 645 times higher than the OXA causes 30% of inhibition. The result indicates the hydroxyl radicals present at the solution may contribute to the degradation of the antibiotic molecules. The essays in the presence of KI concentration 25 times higher than the OXA concentration showed 75% of inhibition. The use of equimolar KI concentration resulted in a 13% reduction. The indication of the degradation rate is in association with adsorption reduction of the catalyst surface. Consequently, the degradation of OXA by heterogeneous photocatalysis seems to occur mostly at the catalyst surface and via two routes: by the radical attack and photo-Kolbe mechanism. The UV irradiation of antibiotic molecules generates excited states and the detection of such reactive species by an indication of their ability to oxidize luminal reagent. Such compound uses the electronically excited aminophthalate, which

for OXA with mannitol, and 1.4 μM min<sup>−</sup><sup>1</sup>

for

sonochemical processes' removal of oxacillin from polluted water.

for OXA, 1.3 μM min<sup>−</sup><sup>1</sup>

**80**

**Figure 2.** *Oxacillin photodegradation pathway.*

decays to the ground state releasing electromagnetic radiation in the visible zone of the spectrum—the application of the method to penicillin G, nafcillin, azlocillin, and neomycin dissolved in water. The intensity of the luminal chemiluminescence emission (CL) was proportional to the radical concentration and dependent on the molecular structure of the drugs. Under the optimized conditions, the penicillin and azlocillin were the most susceptible to photodegradation, while neomycin sulfate was less affected by the UV light. The addition of a hydroalcoholic extract of rose petals to antibiotic solutions reduced the CL intensity, indicating the alcohol act as a scavenger of free radicals of the irradiated drugs.

## **10. Synergistic effect**

In the application of the solar photodecomposition in the dye mixture of RH and MB, the result is similar with a single dye, and the adsorption balance remains unchanged with no interaction between RH and MB and their by-products. Nevertheless, the addition of MO in the mixture accelerated the photodecomposition significantly. The decomposition of RH/MO and the MB/MO reduced the decomposition time in 13 and 10 min, respectively [21]. Such an effect is positively dependent on the MO concentration; the application of Eq. (23) to the Langmuir-Hinshelwood model

$$-\ln\left(\text{C}/\text{C}\_{o}\right) = \dot{\text{k}}^{\cdot}\text{Kt} = \text{kt} \tag{23}$$

where Co and C are the initial and t measured concentrations, t is the reaction time, and k are the first-order-kinetic reaction constant, calculated using log(C/Co) vs. t.

The kinetics k rate indicates higher values for binary systems with MO component. When the MO concentration reaches a constant value, the reaction depends on the photocatalyst mass. The preparation of ternary mixtures with RH or MB and different azo species as orange G (OG), methyl red (MR), and Eriochrome Black T (EBT) clarifies the reaction mechanism dependency. The synergistic effect after azo compound addition is confirmed, and the time decreases about 23 and 13 min for RH and MB, respectively.

The photodecomposition acceleration effect is positively proportional to the azo dye concentration and no longer changes after reaching a specific equilibrium value. The comparison with the k values indicates higher rates for EBT > OG > MO > MR; the sequence is in agreement with the polarity of the four azo dye compounds. The azo compounds in the experiments were acid orange 7 (AO7), Congo red (CR), and amido black 10B (AB10B). The results were the same obtained for the other azo compounds confirming the synergistic oxidation effect.

The possible decomposition mechanism includes the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) as a type of molecular frontier orbitals. Roughly, the HOMO level is for organic semiconductors, the equivalent of the valence band for the inorganic semiconductors, and the LUMO is the equivalent of the semiconductors' conduction band. The energy difference between them is called a HOMO-LUMO gap. The energy gap between the two frontier orbitals can be used to predict the strength and stability of the transition metal complexes and also their colors in solution.

The simulated changes of the azo molecule methylene orange (MO) in molecular energy structure in the photocatalyst Ag2O surface indicate the LUMO composed by the atomic orbital contributions of benzene, nitrogen, and the nitrogen double bond, and the HOMO is a result of the paired electron orbits of negatively charged oxygen atoms in the sulfonic group.

After the MO adsorption in Ag2O surface, the electrons on the surface of the Ag2O can transfer to the molecules' LUMO and participate in feedback coordination at the bond. The C▬N bond links the benzene ring to the azo group, and it becomes longer on adsorption. Such coordination effects weaken the π bonding conjugated over the whole molecular skeleton and start to be attacked by photogenerated electrons or radicals, with the presence of active fragmented intermediates. The resultant intermediates caused subsequent acceleration of azo bond cleavage also for non-azo organic cleavages due to their oxidative activity.

The infrared results of the MO adsorbed in Ag2O indicate a shift for N〓N bond from 1392 to 1396 cm<sup>−</sup><sup>1</sup> , for -SO3<sup>−</sup> was observed from 1314 and 1121 cm<sup>−</sup><sup>1</sup> to 1320 and 1120 cm<sup>−</sup><sup>1</sup> , and for C▬N bonds from 817 and 749 cm<sup>−</sup><sup>1</sup> to 819 and 751 cm<sup>−</sup><sup>1</sup> . Another shift for Ag2O was from 650 to 705 cm<sup>−</sup><sup>1</sup> . They are the confirmation of the sulfonic group acting as an electron donor and Ag2O as an electron acceptor, weakening the conjugated π bonding and activating the N〓N and C▬N bonds confirming the adsorption of MO by Ag2O. The MO peaks disappear including the sulfonic group and the azo bond after 2 min of irradiation, suggesting to be the first degraded group. The suspension started to be colorless, and the peaks assigned to be C〓C bond start to appear after 5 min of exposition, an indication of the benzene rings broken. There is no observation of MO chemical structure after 10 min of light irradiation; it is an indication of the complete dye decomposition. The azo bond or C▬N bond connected with the benzene rings broken first and produces active intermediates which accelerate the degradation of non-azo organics followed by the benzene ring broken.

Generally, the C▬N bond linked to the benzene ring and the azo group of the MO is the first target for the free radicals produced by the photocatalyst. The possible intermediates are aminobenzenesulfonates, aromatic amines, phenolic

**83**

suspension. The ions HCO3

<sup>−</sup>/CO3

<sup>2</sup><sup>−</sup>, SO4

<sup>2</sup><sup>−</sup>, Cl<sup>−</sup> and NO3

<sup>−</sup> showed inhibitory effects

*Green Water Treatment for Pharmaceutical Pollution DOI: http://dx.doi.org/10.5772/intechopen.85116*

<sup>−</sup>, NH4

wastewater with a complex dye mixture.

<sup>−</sup>, and NO3

N2, CO2, H2O, SO4

in the Ag2O surface.

**11. Conclusion**

compounds, and organic acids. The final products, also called mineralization, are

The presence of photodecomposition intermediates to the photodegradation process of RH and Ag2O resulted in faster decomposition. The phenol addition reduces the decomposition time to 8 min, the sulfanilic acid in 10 min, and the benzoquinone in 30 min. However, the addition of acetic acid and hydroquinone slows the RH photodegradation. Finally, the MO molecule can be decomposed into holes or radicals generated over Ag2O and break the C▬N bonds releasing the benzene containing the intermediates such as benzene sulfonate and N-N dimethylaniline. The next intermediate products were hydroxybenzenesulfonate activated by excited Ag2O and diffused in solution accelerating the degradation of organic compounds

The description of the acceleration of the photodegradation process with azo dyes' presence in a mixed dye solution is a synergy between the azo structure and Ag2O with the generation of aniline, sulfanilic acid, and phenol compounds which also accelerates the degradation of the non-azo compounds. The synergetic effect is beneficial for the Ag2O photodecomposition applicability to treat the ordinary real

Environmental sustainability demands the advance in water treatment and the use of lighting natural resources. Brazil has one of the most stable and intense solar irradiation in the word. It has to be used not only for energy generation purposes but also and mostly for water treatment, water quality polishment, and furthermore water disinfection. The chapter performs a comparison of different green technologies for water treatment as natural solar irradiation. The photocatalytic hydroxide radicals are the photodecomposition potent oxidants and react fast and unselectively with surrounding chemical species via radical addition, hydrogen abstraction, or e<sup>−</sup> transfer mechanisms. The transformation by-products of pharmaceuticals and EDC compounds (TBPs) with higher photodecomposition effectiveness ends up in complete mineralization with the production of CO2, H2O, and inorganic salts. The heterogeneous photocatalysis shows a strong dependence of the operating temperature, and the kinetics is usually dependent on the first step of the adsorption and the equilibrium modeled by Langmuir isotherms and Langmuir-Hinshelwood model. The first pseudo-order usually appears at the beginning of the reaction, just in the initial steps, and as the reaction proceeds, the intermediates' production could interfere with the radiation incidence. There is a competition of the adsorption sites of the catalyzer surface between the pollutant and others adsorbed species; the pollutants start concentration is a limiting reactant step with mass transfer limitations in lower concentrations. The semiconductor TiO2 photocatalytic process has shown great potential as a low cost, environment-friendly treatment technology in degrading a wide range of pollutants with the formation of reactive oxygen species upon excitation of a semiconductor particle with light energy greater than the respective bandgap energy of the photocatalyst. The photocatalyst TiO2 has superior characteristics over others with wide bandgap energy which requires the UV light which is 3–5% of natural solar light. The application of a variety of strategies improved the photocatalytic efficiencies from photocatalysts as dispersed solids to second-generation photocatalysts (chemically doped and physically modified dispersed solids) achieving better spectral sensitivity and photoactivity. Many studies indicate the scavengers' presence reduces the photodecomposition effect in water

−.

compounds, and organic acids. The final products, also called mineralization, are N2, CO2, H2O, SO4 <sup>−</sup>, NH4 <sup>−</sup>, and NO3 −.

The presence of photodecomposition intermediates to the photodegradation process of RH and Ag2O resulted in faster decomposition. The phenol addition reduces the decomposition time to 8 min, the sulfanilic acid in 10 min, and the benzoquinone in 30 min. However, the addition of acetic acid and hydroquinone slows the RH photodegradation. Finally, the MO molecule can be decomposed into holes or radicals generated over Ag2O and break the C▬N bonds releasing the benzene containing the intermediates such as benzene sulfonate and N-N dimethylaniline. The next intermediate products were hydroxybenzenesulfonate activated by excited Ag2O and diffused in solution accelerating the degradation of organic compounds in the Ag2O surface.

The description of the acceleration of the photodegradation process with azo dyes' presence in a mixed dye solution is a synergy between the azo structure and Ag2O with the generation of aniline, sulfanilic acid, and phenol compounds which also accelerates the degradation of the non-azo compounds. The synergetic effect is beneficial for the Ag2O photodecomposition applicability to treat the ordinary real wastewater with a complex dye mixture.
