**3. Semiconductor materials**

Semiconductor photocatalytic process has shown great potential as a low cost, environment-friendly treatment technology in degrading a wide range of pollutants. The photocatalysis has the dependency of the reactive oxygen species formation by the semiconductor particle with light energy greater than the bandgap energy [4]. The TiO2 photocatalyst has an important drawback of photocatalysis and with gap energy which is the use of UV light, corresponding with 3–5% of natural solar light.

Some modification on TiO2 surface is one promising route to enable TiO2 sensitive to visible light for water purification. A variety of strategies improve the photocatalytic efficiency from dispersed solids to second-generation photocatalysts (chemically doped and physically modified by dispersed solids) achieving better spectral sensitivity and photoactivity.

Published results indicate better results with inert materials as zeolite (TiO2-FeZ) or TiO2 (SnS2). Zeolite showed high surface area but lower bandgaps in comparison with TiO2 powder and decreases the efficiency following the FeZ and SnS2 content [5]. The H2O2 addition enhanced solar-driven degradation and solar/TiO2-FeZ with higher decomposition rates followed by solar/TiO2-SnS2 with 51%, TiO2 P25 with 41.3%, and finally 34.4% for TiO2-SnS2/H2O2. The pseudo-first-order kinetics was the driving for solar photodecomposition with the higher rates for solar/TiO2-FeZ/ H2O2 with K1 = 15.39×10<sup>−</sup><sup>3</sup> min<sup>−</sup><sup>1</sup> with more than twice of the solar/TiO2-SnS2 rate and three times more than solar/TiO2, solar/TiO2/H2O2, and solar/TiO2-SnS2/H2O2.

A challenge to be overcome is the presence of suspended solid particles in the reaction environment; they reduce the solar irradiance and the photocatalysis efficiency. The solid deposition over an inert material with the high surface area can fix and stabilize the solid particles. The engineering materials with transitional metals in surface deposition are a solution, like carbon nanotubes, dye sensitizers, conductive polymers, graphene oxide, and other semiconducting materials. The semiconductor supporting material has to avoid the agglomeration formation.

The commercial TiO2 (P25) is the most common catalyzer in spite of lower azo decomposition; Ag2O is another active photocatalyst with promising results for azo photodecomposition. Nevertheless, the use of Ag2O in azo mixture showed faster degradation with better decomposition results due to the synergetic oxidation effect.

The scavengers' presence reduces the photodecomposition effect in water 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 toward the hydroxyl radicals generated by AOPs.

The natural organic matter (NOM) presence showed a synergistic effect increasing the E2 degradation, such degradation produces other radicals. Published studies relate to the degradation of the NOM species of humic acid and fulvic acid applied in solar/photodegradation resulting in all organic compounds that were mineralized after 150 min of treatment. The formed E2 intermediaries during the treatment do not possess any estrogen effect.

The addition of noble metals as Au and Ag increases the visible light ability with the manipulation of the optical properties and microstructure combined with inorganic and biotemplates as nanostructures of micelles, as spent tea leaf, trimethylammonium bromide, and metal nanoparticles improve the photodegradation efficiency. The use of Co3O4 spinel nanoparticles, NiO nano-sticks, the binary metal oxide nanocomposites of CeO2/Y2O3 and NiO/MnO is effective in dye degradation of RhB, MB, MO, and rose bengal dye.

BiOCl has superior efficiency as photocatalysts due to the interlayer-specific structure of [Bi2O2]2 + with double Cl<sup>−</sup> ions where the photogenerated e<sup>−</sup> and h+ pairs are separated. The BiOCl microspheres synthesized via ethylene glycol are mediated

**71**

and alkaline conditions.

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

> − and h+

(0.0935 min<sup>−</sup><sup>1</sup>

worldwide.

separation of photogenerated e<sup>−</sup>

**4. Dye photodecomposition**

and holes showed the ˙O2

by a solvothermal method with the visible light drive. The crystallinity, surface area, and optical and electronic properties of BiOCl samples depend on the reactant concentration with the benefit from the exposed (110) face and oxygen vacancy; BiOCl allows a maximum CBZ degradation efficiency of 70% after 180 min under visible light illumination. The kinetic rate constant (k) of CBZ degradation in synthetic BiOCl

) was 52 times higher than the ordinary BiOCl (0.0018 min<sup>−</sup><sup>1</sup>

most important; the BiOCl performance was also efficient in natural water without any additive. The experimental findings indicate the BiOCl photocatalysis is an efficient and cost-effective technology for recalcitrant pharmaceutical contaminant removal.

The higher development of the textile industry caused the emission of large quantities of dye wastewater with high chemical stability in surface water resources all over the world; the effect is the severe environmental damage and problems

The advanced oxidation process (AOP) is in situ treatment technology and is widely applied on persistent, toxic, and poorly biodegradable organic pollutants. The improvement of photodecomposition process reduces the by-products' and final products' toxicity. The biological methods are insufficient to decompose such stable organic compounds and chemical molecules. Industrial wastewater is a mixture of various components with high complexity and diversity. The interactions among the different components can occur, weakening and even blocking the photodecomposition effect. The heterogeneous photocatalysis is taking considerable attention to the textile wastewater treatment due to its low cost and low secondary by-product pollution. The disadvantages are the low quantum efficiency and slow reactant rate using the most common semiconductor, the TiO2. The use of Ag2O with a very narrow bandgap of 1.3 eV allows applying a wide range of the solar spectrum with an increase in the photodecomposition rate. The literature describes a photodecomposition process with last about 120 s to degrade the Methyl

orange under UV and Visible light and 40 min with only Infrared light.

99.5% of MB using 4, 50, and 20 min, respectively.

The application of the visible light photodecomposition in a dye mixture of methylene blue (MB), methyl orange (MO), and rhodamine (RH) indicates the MO as the more stable azo compound than the other organic pollutants due to the aromatic groups attached at the end of the azo bond. Despite this fact when the light-driven photodecomposition uses Ag2O as a catalyzer, it was the fastest and easiest decomposed compound. Published results indicate the visible light photodecomposition with Ag2O with the elimination of 90.2% of MO, 96.5% of RH, and

In dye photodecomposition in acidic conditions, some peaks with higher absorbances change some wavelength numbers indicating the chemical structure transformation from hydrazone to azo form. Despite such change, the concentration still reduces with time, and the complete degradation of the dye mixture finished in 18 min at pH 3 and 15 min at pH 5. The observation of 90% of the total mineralization was after 50 min under acidic conditions and 40 min under neutral

The dye mixture showed better decomposition results than only a single one; a synergistic oxidation phenomenon occurring in the photodegradation of the dye

pairs. The trapping experiments of radicals

as dominant active species in the process and the

improved photocatalytic activities for BiOCl were attributed to the combination of enhanced carbamazepine adsorption, increased with visible light drive and efficient

and h+

). The

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

*Green Chemistry Applications*

natural solar light.

**3. Semiconductor materials**

spectral sensitivity and photoactivity.

min<sup>−</sup><sup>1</sup>

<sup>−</sup>/CO3

toward the hydroxyl radicals generated by AOPs.

<sup>2</sup><sup>−</sup>, SO4

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

The natural organic matter (NOM) presence showed a synergistic effect increasing the E2 degradation, such degradation produces other radicals. Published studies relate to the degradation of the NOM species of humic acid and fulvic acid applied in solar/photodegradation resulting in all organic compounds that were mineralized after 150 min of treatment. The formed E2 intermediaries during the treatment do

The addition of noble metals as Au and Ag increases the visible light ability with the manipulation of the optical properties and microstructure combined with inorganic and biotemplates as nanostructures of micelles, as spent tea leaf, trimethylammonium bromide, and metal nanoparticles improve the photodegradation efficiency. The use of Co3O4 spinel nanoparticles, NiO nano-sticks, the binary metal oxide nanocomposites of CeO2/Y2O3 and NiO/MnO is effective in dye degradation

BiOCl has superior efficiency as photocatalysts due to the interlayer-specific

are separated. The BiOCl microspheres synthesized via ethylene glycol are mediated

ions where the photogenerated e<sup>−</sup>

H2O2 with K1 = 15.39×10<sup>−</sup><sup>3</sup>

suspension. The ions HCO3

not possess any estrogen effect.

of RhB, MB, MO, and rose bengal dye.

+

with double Cl<sup>−</sup>

structure of [Bi2O2]2

Semiconductor photocatalytic process has shown great potential as a low cost, environment-friendly treatment technology in degrading a wide range of pollutants. The photocatalysis has the dependency of the reactive oxygen species formation by the semiconductor particle with light energy greater than the bandgap energy [4]. The TiO2 photocatalyst has an important drawback of photocatalysis and with gap energy which is the use of UV light, corresponding with 3–5% of

Some modification on TiO2 surface is one promising route to enable TiO2 sensitive to visible light for water purification. A variety of strategies improve the photocatalytic efficiency from dispersed solids to second-generation photocatalysts (chemically doped and physically modified by dispersed solids) achieving better

Published results indicate better results with inert materials as zeolite (TiO2-FeZ) or TiO2 (SnS2). Zeolite showed high surface area but lower bandgaps in comparison with TiO2 powder and decreases the efficiency following the FeZ and SnS2 content [5]. The H2O2 addition enhanced solar-driven degradation and solar/TiO2-FeZ with higher decomposition rates followed by solar/TiO2-SnS2 with 51%, TiO2 P25 with 41.3%, and finally 34.4% for TiO2-SnS2/H2O2. The pseudo-first-order kinetics was the driving for solar photodecomposition with the higher rates for solar/TiO2-FeZ/

and three times more than solar/TiO2, solar/TiO2/H2O2, and solar/TiO2-SnS2/H2O2. A challenge to be overcome is the presence of suspended solid particles in the reaction environment; they reduce the solar irradiance and the photocatalysis efficiency. The solid deposition over an inert material with the high surface area can fix and stabilize the solid particles. The engineering materials with transitional metals in surface deposition are a solution, like carbon nanotubes, dye sensitizers, conductive polymers, graphene oxide, and other semiconducting materials. The semiconductor supporting material has to avoid the agglomeration formation. The commercial TiO2 (P25) is the most common catalyzer in spite of lower azo decomposition; Ag2O is another active photocatalyst with promising results for azo photodecomposition. Nevertheless, the use of Ag2O in azo mixture showed faster degradation with better decomposition results due to the synergetic oxidation effect. The scavengers' presence reduces the photodecomposition effect in water

with more than twice of the solar/TiO2-SnS2 rate

<sup>−</sup> showed inhibitory effects

and h+

pairs

**70**

by a solvothermal method with the visible light drive. The crystallinity, surface area, and optical and electronic properties of BiOCl samples depend on the reactant concentration with the benefit from the exposed (110) face and oxygen vacancy; BiOCl allows a maximum CBZ degradation efficiency of 70% after 180 min under visible light illumination. The kinetic rate constant (k) of CBZ degradation in synthetic BiOCl (0.0935 min<sup>−</sup><sup>1</sup> ) was 52 times higher than the ordinary BiOCl (0.0018 min<sup>−</sup><sup>1</sup> ). The improved photocatalytic activities for BiOCl were attributed to the combination of enhanced carbamazepine adsorption, increased with visible light drive and efficient separation of photogenerated e<sup>−</sup> and h+ pairs. The trapping experiments of radicals and holes showed the ˙O2 − and h+ as dominant active species in the process and the most important; the BiOCl performance was also efficient in natural water without any additive. The experimental findings indicate the BiOCl photocatalysis is an efficient and cost-effective technology for recalcitrant pharmaceutical contaminant removal.

## **4. Dye photodecomposition**

The higher development of the textile industry caused the emission of large quantities of dye wastewater with high chemical stability in surface water resources all over the world; the effect is the severe environmental damage and problems worldwide.

The advanced oxidation process (AOP) is in situ treatment technology and is widely applied on persistent, toxic, and poorly biodegradable organic pollutants.

The improvement of photodecomposition process reduces the by-products' and final products' toxicity. The biological methods are insufficient to decompose such stable organic compounds and chemical molecules. Industrial wastewater is a mixture of various components with high complexity and diversity. The interactions among the different components can occur, weakening and even blocking the photodecomposition effect. The heterogeneous photocatalysis is taking considerable attention to the textile wastewater treatment due to its low cost and low secondary by-product pollution. The disadvantages are the low quantum efficiency and slow reactant rate using the most common semiconductor, the TiO2. The use of Ag2O with a very narrow bandgap of 1.3 eV allows applying a wide range of the solar spectrum with an increase in the photodecomposition rate. The literature describes a photodecomposition process with last about 120 s to degrade the Methyl orange under UV and Visible light and 40 min with only Infrared light.

The application of the visible light photodecomposition in a dye mixture of methylene blue (MB), methyl orange (MO), and rhodamine (RH) indicates the MO as the more stable azo compound than the other organic pollutants due to the aromatic groups attached at the end of the azo bond. Despite this fact when the light-driven photodecomposition uses Ag2O as a catalyzer, it was the fastest and easiest decomposed compound. Published results indicate the visible light photodecomposition with Ag2O with the elimination of 90.2% of MO, 96.5% of RH, and 99.5% of MB using 4, 50, and 20 min, respectively.

In dye photodecomposition in acidic conditions, some peaks with higher absorbances change some wavelength numbers indicating the chemical structure transformation from hydrazone to azo form. Despite such change, the concentration still reduces with time, and the complete degradation of the dye mixture finished in 18 min at pH 3 and 15 min at pH 5. The observation of 90% of the total mineralization was after 50 min under acidic conditions and 40 min under neutral and alkaline conditions.

The dye mixture showed better decomposition results than only a single one; a synergistic oxidation phenomenon occurring in the photodegradation of the dye

mixtures with Ag2O indicates no apparent photoreduction of Ag2O, and the solid material still consisted of pure Ag2O and can be used consequently as a high-performance catalyst for dye wastewater treatment.
