**5. Applications of biological properties**

The applications of nanotechnology in various medical areas, especially in drug delivery have been extensively explored lately. Considering the ultra-small (1–100 nm) and controllable size, high surface-to-mass ratio and high reactivity of NPs, they easily interact with biological systems [46].

The nanosized spinel ferrites and transition metal-substituted ferrites could successfully substitute some antibiotics that are currently used to combat pathogenic bacteria in the gastrointestinal tract of animals, as well as other biomedical applications. Many studies reported the synthesis and characterization of transition metal substituted Co ferrite NPs, but the attention dedicated to their biocompatibility in view of *in vivo* biomedical applications to assure their safe clinical use is still limited. The key criteria for their clinical applications are good biocompatibility and safety [47].

The use of magnetic nanoparticles in biomedical applications demands appropriate shape and size, high magnetization, good ability to deliver the pharmacologically active compounds, non-toxicity and biodegradability. The overall biocompatibility of Co0.5M0.5Fe2O4 (M = Cu, Zn, Mn, Ni) NPs synthetized by the sol-gel process using citric acid as chelating agent decreased in the following order: Co0.5Mn0.5Fe2O4 < Co0.5Cu0.5Fe2O4 < Co0.5Zn0.5Fe2O4 < Co0.5Ni0.5Fe2O4. The biocompatibility of NPs depended on the toxicity of transition metal and the releasing rate of transition metal ions into the cell culture medium [48]. Some possible mechanisms of magnetic NP-based antimicrobial drug delivery to microorganisms could be: (*i*) the NPs fuse with microbial cell wall or membrane and release the carried drugs into the bacteria cell; (*ii*) the NPs bind to cell wall and continuously release the drug, which diffuses into the interior of the microorganisms [49]. Iqbal et al. reported the development of Zn0.5Co0.5Fe2O4 NPs, with the required shape and size, as anti-cancer drug with passive targeting NPs delivering system into cancerous cells by applying photodynamic therapy through controlling the particle size according to the human body (HepG2) cells [40].

The applications of ferrites in tissue engineering are limited due to their inertness towards bioactivity and release of some toxic elements into the human body fluid. However, the migration can be controlled by encapsulation of ferrite NPs by glass matrix. The addition of bioglass in the ferrite displays some biodegradability and supports better osteoblasts growth *in vitro*. In this regard, the bioactive glass containing Co0.2Cu0.8Fe2O4 prepared using self-propagating high-temperature synthesis, showed good potential in bone hyperthermia application [50]. In magnetic hyperthermia, the ferrite NPs are used as local heat dissolving agents in external magnetic field. After their introduction into the body through blood, the body's immune system identifies them as foreign substances and the body rejects the material. To overcome this problem, the

**57**

photocatalyst activity [62].

*Progress, Challenges and Opportunities in Divalent Transition Metal-Doped Cobalt Ferrites…*

biocompatible surface-coating (i.e. chitosan) helps to stabilize the ferrite NPs and provides an available surface area for the biomolecular conjugation for biomedical applications [51]. In this regard, the study of the effect of chitosancoated Co1−xMnxFe2O4 (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) NPs obtained via wet chemical co-precipitation on the hyperthermia temperature (directly related to specific loss power for cancer treatment) revealed that Co0.2Mn0.8Fe2O4 exhibited

The catalysts are important players in numerous chemical processes, especially in organic synthesis or decomposition of persistent pollutants. In the last decade, the use of magnetic NPs as catalysts attracted considerable interest due to the enhancement of the reaction speed, possibility of catalyst separation from the reaction medium by using an external magnet, without any filtration or centrifugation, and its reuse or recycling [53, 54]. In this regard, several conventional synthesis methods were replaced with more eco-friendly options that use magnetic nanosized catalysts. The catalytic processes that use magnetic NPs as catalysts include decomposition of recalcitrant organics, dehydrogenation, oxidation, alkylation and

The catalytic activity is influenced by the particle size, surface area, morphology, nature and concentration of the catalyst [10, 53]. In spinel ferrites, the presence of cations with different charges determines its catalytic properties as it allow internal redox reactions [55]. The distribution of metal ions between tetrahedral (A) and octahedral (B) sites also influences the catalytic activity. Thus, by doping transition metal ions in the ferrite structure, the cationic distribution is changed

One of the main applications of magnetic NPs as catalysts is in the photocatalytic degradation or organics in the presence of visible or UV light. The photocatalytic activity of NPs is based on their capacity to efficiently absorb photons, that excite electrons from the valence band into the conduction band, leaving positively charged vacancy to react with the water molecules and to generate active radicals such are hydroxyl (·OH) or superoxide (·O2) that further react with the pollutants [56]. Beside the ability to absorb photons, the reusability, recyclability, low cost, chemical stability and high corrosion resistance are important factors in the selection of photocatalysts [57]. The crystallite size, surface area, band gap, cations distribution among tetrahedral (A) and octahedral (B) sites and magnetic proper-

In the last decades, a wide range of non-biodegradable organic dyes, inks and pigments were identified in wastewaters from the leather, textile, printing, paper, food and cosmetics industries. These dyes may pose carcinogenic and mutagenic risks and are difficult to treat using conventional water treatment methods.

Nanosized Co ferrite is a magnetic material with high *HC* and moderate *MS*, narrow band gap, low toxicity, low price and good catalytic activity [10, 58]. By doping, its structural and catalytic properties may be further enhanced. The doped and codoped Co ferrites are promising catalysts that may decompose recalcitrant organic chemicals from wastewaters or enhance the synthesis of organics [9, 52, 56, 59–61]. The doping of transition metal ions (Cr, Mn, Co, Zn) into the spinel lattice of Co ferrite influences the physicochemical properties and improves their stability [11]. Moreover, the doping favors the formation of mixed or inverse spinel structures and introduces new donor or acceptor levels, which boosts the visible light activated

*DOI: http://dx.doi.org/10.5772/intechopen.93298*

**6. Applications of catalytic activity**

resulting in modified catalytic activity [10].

ties are influenced by the dopant type and amount [10, 43].

hyperthermia range [52].

coupling reactions [9, 54].

*Progress, Challenges and Opportunities in Divalent Transition Metal-Doped Cobalt Ferrites… DOI: http://dx.doi.org/10.5772/intechopen.93298*

biocompatible surface-coating (i.e. chitosan) helps to stabilize the ferrite NPs and provides an available surface area for the biomolecular conjugation for biomedical applications [51]. In this regard, the study of the effect of chitosancoated Co1−xMnxFe2O4 (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) NPs obtained via wet chemical co-precipitation on the hyperthermia temperature (directly related to specific loss power for cancer treatment) revealed that Co0.2Mn0.8Fe2O4 exhibited hyperthermia range [52].
