Читать книгу Functionalized Nanomaterials for Catalytic Application - Группа авторов - Страница 15

Fenton’s redox chemistry employs ^·OH released between the reacting species (H₂O₂ + Fe²⁺) 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 H₂O₂ → ^·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 Fe₂O₃/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 - Fe₃O₄/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 Fe₃O₄@Fe₂O₃/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 Fe²⁺ aided the decomposition of peroxide to form ^·OH. ^·OH and ^·O²⁻ contribute for the degradation of OP. Mesoporous FNMs MnCo₂O₄-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]. Mn²⁺/Mn³⁺, Co³⁺/Co²⁺ 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.

FNMs as catalyst | Type | Year	Process | Current/Voltage	Parametric expressions	Solution evolved (% degradation) | Reusable cycles	Remarks	Ref.
BGA-GDE | EF | 2019	Hydrothermal | 4.5 mA cm−2	pH (3–9) | 60 min	BPA (~89.65%) | 5 TOC (~90%) | 5	· OH | pseudo-1st-order kinetics	[62]
RGO-Ce/WO3 NS/CF | EF | 2018	Hydrothermal | 300–400 mA	pH (3) | 1h	CIP (100%) | 5	· O2−, H2O2, ·OH | Ce-WO3 improved adsorption	[63]
ACF-HPC | EF | 2019	Hydrothermal, carbonization | (16, 20, 24) mA cm−2	pH (3, 7, 9) | 40, 180 min	Phenol (93.8%) | 5TOC (85.7%) | 5	Enhanced formation of H2O2, ·OH | Low-cost	[64]
Fe-C/PTFE | H-EF | 2015	Ultra-sonification | 100 mA	pH (6.7) |120 min	2,4-DCP (95%) |	pseudo-1st-order kinetics | promoters: H2O2, ·OH | Cheap	[65]
N-C (NF) as (c PANI/GF2) | EF | 2019	Carbonization (PANI) |−0.6 V	pH (3) |180 min	Mineralization (42%) | Florfenicol (99%)| Phenol (85%) | MO (100%) | 5	Activation: H2O2 → ·OH	[66]
FeOx/NHPC750 | H-EF | 2020	Hydrothermal, carbonization | (−3.30, −4.42, −3.77) mA cm−2 | −0.6 V	pH (6) |90 min	ATZ (96%) | Rh B (99%) | 2,4-DCP (99%) | Sulfamethoxazole (95%) | Phenol (99%) | 5	Cleavage of O-O bond | Assists H2O2 | Fe2+ + O2 → Fe3+ + ·O2−	[67]
(Co, S, P)/MWCNTs | P-EF |2019	Hydrothermal | 40 mA cm−2	pH (3) |360 min	Bronopol (100%) |TOC (77%) | 3	Contributors: sunlight, ·OH, BDD (·OH) |	[68]
Mn/Fe@porous C (PC)-CP cathode | H-EF | 2019	Carbonization | 40 mA	pH (2–8) |120 min, 240 min	TCS (100%) | TOC (~57%) | 6	Regeneration: Fe2+/Mn2+/3+| e-transfer: Fe2+/3+, Mn2+/3+/4+, pseudo-0-order kinetics	[69]
3DG/Cu@C | H-EF | 2020	Hydrothermal, calcination | 30 mA	pH (3–9) | 150 min	Rh B (100%) | CIP (100%) | 2,4-DCP (100%) | PCA (89.8%) | BPA (96.1%) | CAP (82.6%) | 5	Contributors: ·OH, ·O2− | e- transfer: Cu2+/+	[70]
C felt/Fe-Oxides | H-EF | P-EF | 2016	Electro-deposition | 21.7 mA cm−2	pH (3) |120 min	MG (98%) | 10	·OH, BDD - activators | UVA | pseudo-1st-order kinetics |	[71]
(N-G@CNT | EF | 2108	Hydrothermal | variable | −0.2 V	pH (3) |180 min	DMP (100%) | 20TOC (40.4%)	Fe2+ + H2O2 → Fe3+ + e− | pseudo-1st-order kinetics	[72]
F-rGO/SS membrane | EF | 2019	Electrophoretic deposition | 170 mA | −0.5 V	pH (3) |	PCM (37%) | 5	e- transfer-enhanced by rGO | low-cost membrane	[73]
G-CNT-CE | EF | 2014	Electrophoretic deposition | 0.18 A	pH (3) |210 min	Acid Red 14 (91.22%) |Acid Blue 92 (93.45%)	pseudo-1st-order kinetics | pseudo-2nd-order kinetics	[74]
Fc-ErGO | EF | 2018	Electrochemical | −1.5 V | (−0.75, −1.0, −1.5, −2.5) V	pH (3) | 15 min | pH (7) | 120 Min	CIP (99%) | 5	·OH | pseudo-1st-order kinetics	[75]
FeOCl-CNT | EF | 2020	Thermal-induced | −0.8 V	pH (wide) |	TC (99.5%) |	Fe3+/Fe2+ | H2O2 + ·OH → H2O + ·OOH	[76]
3D GA/Ti wire | EF | 2018	Hydrothermal | [0 – (−95.5)] mA cm−2	pH (2) |120 min	EDTA-Ni (m73.2%) | 5	π-π interaction | pseudo-1st- order kinetics	[77]

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 (Fe²⁺/Fe³⁺) 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@Fe₃O₄” 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 Fe₃O₄ on 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 1.1 depicts trials developed by some research personalities.