Functionalized Nanomaterials for Catalytic Application

Figure 1.2 Electrocatalytic degradative action to protect the water system.

Fenton’s redox chemistry employs ·OH released between the reacting species (H 2O 2+ Fe 2+) for the decomposition of target pollutants (TPs), where electro-Fenton (EF) or photoelectro Fenton (P-EF) have prominent roles. Hetero-EF (H-EF) utilizes solid nanocatalyst as a supporter for reducing H 2O 2→ ·OH. The disadvantage of small pH range (acidic) is overcome by solid supporters when used. The effluents released into the water system have a wide range of pH [47]. Micro-porous/meso-porous FNMs offer best solutions for degrading OPs in the water bodies. Research communities are focusing on this segment for protection of environmental crises using Fe/other transition metal/metal oxides as cathodic FNMs in H-EF methods.

Cathodic FNMs are got by (i) uni/multi step synthesis of low-density porous-solids (C aerogels), (ii) modified conducting FNMs with Fe, and (iii) carbonaceous solids supported with Fe or other components as FNMs [48–50]. Formation of sludge as Fe-hydroxides, as in normal Fentons, is retarded or inhibited, thus improving the efficiency and availability of catalyst for its activity. Hence, less energy utilization and a cost-effective approach is favored. Similarly, reusability and recyclability for many trials were observed while using cathodic FNMs of Fe 2O 3/N-C by [51] and Fe-Cu-C aerogel [52]. However, Fe when strengthened with other metals (transition) embedded in it, results in a redox reaction with catalytic decomposition, and is favored with the increase in efficacy of the electrocatalytic system to bring about degradation of TPs [53–55]. A figurative description of the functionalized catalytic activity is shown in Figure 1.3.

In a typical report of Cui, L. et al ., MO decomposition by H-EF was proved to be accelerated by FNM - Fe 3O 4/MWCNTs, when prepared by solvothermal process. Degradability of the TP was noted to be 90.3% (3 h) with reusability to 5 runs, at pH (3). This system with two compartments of FNM membrane required no external additives, but had a potency in green wastewater treatment techniques [56]. Zhao, H. et al . reported that Fe 3O 4@Fe 2O 3/ACA (activated C aerogel) as cathodic in this EF routine degraded (90%) of OP-pesticide imidacloprid (30 min) and TOC (60 min) in pH range of (3–9) [57]. Haber-Weiss model inferred that Fe 2+aided the decomposition of peroxide to form ·OH. ·OH and ·O 2−contribute for the degradation of OP. Mesoporous FNMs MnCo 2O 4-CF (C felt) as cathodic EF with excellent porosity and large modified surface area prepared showed a powerful degrading capacity for CIP (100%) an antibiotic in 5 h and TOC (75%) in 6 h [58]. Mn 2+/Mn 3+, Co 3+/Co 2+with e −transfers enhanced peroxide decomposition to form ·OH and ·OOH required for five cycles degradation.

Figure 1.3 Electro-Fenton functionalized catalytic degradative activity for water bodies.

Table 1.1 Electro-Fenton (EF)/Hetero-Electro-Fenton (H-EF) catalyst as FNMs.

H-EF system with Fe oxides surrounded by Cu and N on HPC (hollow porous C) as cathodic FeO x/CuN xHPC was inferred to give a good degradability for phenol (100%/90 min/variable pH) and (81%/120 min/pH6). Slow redox reaction (Fe 2+/Fe 3+) favored e −movement, and formation of ·OH, that were essentials for degradation in this ambient condition [59]. In a similar fashion a three-layered H-EF catalyst as FMN “CFP@PANI@Fe 3O 4” engineered using electrodeposition-solvothermal method was proven for the removal of 4-NP (100%/60 min/4 runs) at an acidic pH (3) and TOC (51.2%/7 runs) at the same pH [60]. Enrichment of electrocatalytic capacity was attributed to formation of Fe 3O 4on the functionalized surface of the conducting layers. Wang, Y. et al . fabricated γ-FeOOH GPCA cathodic EF-catalyst for experimenting the degradability of the antibiotic sulfamethoxazole (~90%/5runs). Twelve degraded products by, hydroxylation, isomerization, and oxidation reactions were identified using chromatographic trials [61]. Table 1.1depicts trials developed by some research personalities.