Metal ferrites-based nanocomposites and nanohybrids for photocatalytic water treatment and electrocatalytic water splitting

Photocatalytic degradation is one of the most promising technologies available for removing a variety of synthetic and organic pollutants from the environmental matrices because of its high catalytic activity, reduced energy consumption, and low total cost. Due to its acceptable bandgap, broad light-harvesting efficiency, significant renewability, and stability, Fe₂O₃ has emerged as a fascinating material for the degradation of organic contaminants as well as numerous dyes. This study thoroughly reviewed the efficiency of Fe₂O₃-based nanocomposite and nanomaterials for water remediation. Iron oxide structure and various synthetic methods are briefly discussed. Additionally, the electrocatalytic application of Fe₂O₃-based nanocomposites, including oxygen evolution reaction, oxygen reduction reaction, hydrogen evolution reaction, and overall water splitting efficiency, was also highlighted to illustrate the great promise of these composites. Finally, the ongoing issues and future prospects are directed to fully reveal the standards of Fe₂O₃-based catalysts. This review is intended to disseminate knowledge for further research on the possible applications of Fe₂O₃ as a photocatalyst and electrocatalyst.

Using egg ovalbumin to synthesize pure α-Fe2O3 and cobalt doped α-Fe2O3: structural, morphological, optical and photocatalytic properties

Nanoparticles of undoped hematite (α-Fe2O3) and Co doped α-Fe2O3 were prepared by a simple, green, and cost-efficient process using Co and Fe chlorides and freshly isolated hen egg white. Several techniques of characterization, such as differential thermal and thermogravimetric analysis (DTA/TG), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), EDS analysis, X-ray diffraction analysis (XRD), and Ultra-violet Visible (UV-Vis) analysis were applied. The incorporation of Co particles into the hematite matrix limits the growth of the α-Fe2O3 crystalline grain and favours the apparition of γ-Fe2O3 phase. SEM analysis reveals that there are no significant morphological differences among α-Fe2O3 and Co-α-Fe2O3 particles, whereas the XPS analysis confirms the existence of Fe and Co particles in the as-prepared samples. The optical study shows a slight reduction of band gap energy for Co doped α-Fe2O3 compared to the non-doped α-Fe2O3, which has shown enhanced visible light adsorption performance. On the other hand, the α-Fe2O3 and Co-α-Fe2O3 nano-photocatalysts with an average crystallite size of 21 and 43 nm respectively, were used to remove the Methylene Blue (MB) dye from aqueous solutions after being exposed to visible light. In a mechanistic study, the radicals OH• and •O2 - were shown to be important in the degradation of MB dye. To optimise the effective parameters on MB dye degradation, the experimental parameters applied in the adsorption experiments, such as pH, photocatalyst dosage, contact time, and temperature, were tested. The optimal conditions were determined as pH = 12, photocatalyst dosage = 0.2 g/L. Degradation efficiency in the optimal conditions is 91.8 % after 120 min of irradiation. The pseudo-first and second orders were used to model the kinetic data. The removal of MB using α-Fe2O3 and Co-α-Fe2O3 photocatalysts matched well with pseudo-second-order reaction kinetics. Furthermore, the thermodynamic study reveals that MB dye adsorption on the Co-Fe2O3 absorbent was an endothermic and spontaneous process.

α-Fe2O3/graphene oxide powder and thin film nanocomposites as peculiar photocatalysts for dye removal from wastewater

In this study, hematite graphene oxide (αFe₂O₃-GO) powder nanocomposites and thin-film hematite graphene oxide (αFe₂O₃-GO) were synthesized for application in the removal of Rhodamine B (RhB) from textile wastewater. αFe₂O₃-GO nanomaterials were placed onto the FTO substrate to form a thin layer of nanocomposites. Different analysis including XRD, FTIR, Raman spectra, XPS, and FESEM were done to analyze the morphology, structure, and properties of the synthesized composites as well as the chemical interactions of αFe₂O₃ with GO. The photocatalytic performance of two synthesized composites was compared with different concentrations of αFe₂O₃-GO. The results showed that powder nanocomposites are more effective than thin-film composites for the removal of RhB dye. αFe₂O₃-GO-5% powder nanocomposites removed over 64% of dye while thin-film nanocomposites had less removal efficiencies with just under 47% removal rate. The reusability test was done for both materials in which αFe₂O₃-GO-5% powder nanocomposites removed a higher rate of dye (up to 63%) in more cycles (6 cycles).

Enhanced Photocatalytic Activity of Cu2O Cabbage/RGO Nanocomposites under Visible Light Irradiation

Towards the utilization of Cu₂O nanomaterial for the degradation of industrial dye pollutants such as methylene blue and methyl orange, the graphene-incorporated Cu₂O nanocomposites (GCC) were developed via a precipitation method. Using Hummers method, the grapheme oxide (GO) was initially synthesized. The varying weight percentages (1-4 wt %) of GO was incorporated along with the precipitation of Cu₂O catalyst. Various characterization techniques such as Fourier-transform infra-red (FT-IR), X-ray diffraction (XRD), UV-visible diffused reflectance (UV-DRS), Raman spectroscopy, thermo gravimetric analysis (TGA), energy-dispersive X-ray analysis (EDX), and electro chemical impedance (EIS) were followed for characterization. The cabbage-like morphology of the developed Cu₂O and its composites were ascertained from field-emission scanning electron microscopy (FESEM) and high-resolution transmission electron microscopy (HR-TEM). In addition, the growth mechanism was also proposed. The results infer that 2 wt % GO-incorporated Cu₂O composites shows the highest value of degradation efficiency (97.9% and 96.1%) for MB and MO at 160 and 220 min, respectively. Further, its catalytic performance over visible region (red shift) was also enhanced to an appreciable extent, when compared with that of other samples.

Magnetic Ti3C2Tx (Mxene) for diclofenac degradation via the ultraviolet/chlorine advanced oxidation process

In this study, a magnetic titanium carbide (Ti₃C₂T_x) MXene was synthesized through a one-step chemical co-precipitation method using ammonium bifluoride as a mild etchant and was investigated for photocatalytic degradation of diclofenac (DCF) via the ultraviolet (UV)/chlorine process. The DCF degradation was enhanced by the generation of active radicals such as the hydroxyl radical and reactive chlorine species compared with that resulting from UV and chlorination treatment alone as well as UV/H₂O₂ processes at pH 7. The first-order rate constant of the UV/chlorine process was 0.1025 min^-1, which is 12.7 and 6.8 times higher than those of the only UV and UV/H₂O₂ processes, respectively. Magnetic nanoparticles on the surfaces of Ti₃C₂T_x sheets not only enhanced the adsorption capacity of the synthesized composite but also increased the rate of electron transfer in solution. In addition, the effects of different operating conditions such as magnetic Ti₃C₂T_x dose, pH, and initial chlorine concentration on DCF degradation were investigated. Magnetic Ti₃C₂T_x showed high stability and photodegradation efficiency during seven consecutive degradation reaction cycles. The derivatives of DCF during the photocatalytic degradation process were also investigated based on the observed intermediate products and a degradation pathway was proposed. Thus the synthesized magnetic Ti₃C₂T_x is a simple and affordable photocatalyst, which can significantly enhance DCF degradation in the UV/chlorine advanced oxidation process.

Facile self-assembly synthesis of γ-Fe2O3 /graphene oxide for enhanced photo-Fenton reaction

A novel self-assembly method was developed to prepare a γ-Fe₂O₃/graphene oxide (GO) heterogeneous catalyst that showed excellent synergy between photocatalysis and Fenton-like reactions. The γ-Fe₂O₃/GO catalyst prepared on the iron plates demonstrated efficient and reproducible catalytic activities for water treatment. It takes only 80 min to degrade 50 mg L^-1 methylene (MB) completely, which is the main non-biodegradable dye in wastewater from the textile industry. The heterogeneous catalyst is stable over a wide range of pH (from 2.0 to 10.2) for MB degradation, and can be easily extracted from solution and repeatedly used with little loss of catalytic activity. The high activity and stability of the catalyst system can be attributed to charge separation between γ-Fe₂O₃ and GO, which could accelerate Fenton-like process and photocatalysis. In addition, the dominant reactive oxidant species responsible for the MB degradation, including the hydroxyl radicals (•OH) and holes (h⁺), were trapped on the surface of the γ-Fe₂O₃/GO composite, as proved by a free-radical quenching experiment. The γ-Fe₂O₃/GO heterogeneous catalyst could potentially provide a solution for removal of non-biodegradable dyes from wastewater in the textile industry.

Assembly of ZnO Nanoparticles on SiO2@α-Fe2O3 Nanocomposites for an Efficient Photo-Fenton Reaction

The SiO2@α-Fe2O3/ZnO metal oxide nanocomposites employed in this study were obtained using the sol-gel method. Their photocatalytic activities were enhanced by photo-Fenton reactions. The metal oxide composite of ZnO and α-Fe2O3 nanoparticles were deposited on the SiO2 nanospheres intended for visible light photocatalysis. Further, the as-synthesized SiO2@α-Fe2O3/ZnO nanocomposites exhibited a robust crystallinity and a high adsorption of dye molecules when compared to SiO2@ZnO and SiO2@α-Fe2O3 nanocomposites, respectively. The experimental results demonstrated a rapid Methylene Blue (MB) degradation among these catalysts within short intervals of time with the addition of α-Fe2O3/ZnO mixed metal oxide catalysts on the SiO2 nanospheres. Finally, a photo-Fenton reaction was implemented to confirm the presence of the hydroxyl (OH) radicals, which are powerful agents used for the degradation of organic pollutants.

Effect of reduced graphene oxide on the structural, optical, adsorption and photocatalytic properties of iron oxide nanoparticles

Effect of reduced graphene oxide on the structural and photocatalytic properties of Fe₂O₃ nanoparticles.