Water pollution and fossil fuels are major issues in the context of climate change. Photocatalysis research is rising to develop green technologies for the remediation of pollutants and for energy production. Photocatalysis converts the light energy as photons into chemical energy using semiconducting materials. Different methods are utilised to synthesise these photocatalytic materials. Metal and coupled metal frameworks are applied for the production of photocatalytic materials. Here we review the synthesis and applications of photocatalysts for environmental decontamination and for production of biodiesel, methanol and hydrogen. Pollutants include dyes, pesticides, herbicides, phenols and antibiotics.

Photocatalysis for removal of environmental pollutants and fuel production: a review

Fabricated novel g-C3N4/Mn doped ZnO nanocomposite as highly active photocatalyst for the disinfection of pathogens and degradation of the organic pollutants from wastewater under sunlight radiations

0D, 1D and 2D nanomaterials for visible photoelectrochemical water splitting. A Review

Designing of highly active g-C3N4/Ni-ZnO photocatalyst nanocomposite for the disinfection and degradation of the organic dye under sunlight radiations

In this study, nickel ferrite nanoparticles (NiFe2O4 NPs) were synthesized via simple and cost effective sonochemical method. X-ray diffraction confirmed the formation of inverse spinel ferrite with face centered cubic structure and the dimensions of the NPs ranged from 9 to 17 nm. Kubelka–Munk function was applied to study diffuse reflectance spectra and the band gap of the NPs was determined as 2.26 eV. Methylene blue (MB) and Drimarene yellow (DY) dyes were used as model dyes to study the photocatalytic properties of NPs under ultraviolet light irradiation. Point of zero charge (pHpzc) has played a significant role in understanding the adsorption of dyes onto the surface of the photocatalyst. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements for NiFe2O4 electrode were performed in 0.1 M HCl and 0.1 M NaOH aqueous electrolytes. The electrode exhibited specific capacitance of 2.084 F g–1 and 0.533 F g–1 in acidic and basic electrolytes, respectively. EIS measurements showed reduction in the charge transfer resistance. Modified carbon paste electrode using NiFe2O4 NPs has sensed Paracetamol in both acidic and alkaline electrolytes. These results indicated that NiFe2O4 is a promising electrode material for sensing paracetamol with high electrode reversibility and is an excellent photocatalyst. Hence, sonochemically synthesized NiFe2O4 NPs are expected to offer significant insight into their multifunctional applications.

Sonochemical synthesis of NiFe2O4 nanoparticles: Characterization and their photocatalytic and electrochemical applications

A new photocatalytic material sodium iron disulfide (NaFeS2) has been synthesized via a hydrothermal method for the degradation of methylene blue (MB) and indigo carmine (IC). This material has been subjected to various analytical, electrochemical and photocatalytic studies to understand its morphology, crystallinity, band gap, oxidation-reduction potential and ability to catalyse the rate of dye degradation. The material exists as nanorods with a thickness of 30–100 nm and a monoclinic phase with an average crystallite size of 25–30 nm. The energy bandgap of the prepared photocatalyst has been calculated using the Kubelka-Munk function and is found to be 2.01 eV. Using a UV light source, the photocatalytic activity of NaFeS2 has been carried out, where the time of irradiation determined the ability of the catalyst to degrade the dye under investigation. With a degradation efficiency of 97% in 105 min for MB and 99% in 45 min for IC, NaFeS2 appears as an excellent photocatalytic material. The electrochemical studies also act as a testament for NaFeS2’sadmirable photocatalytic property. The photocatalytic and electrochemical activities of NaFeS2 offer an innovative platform for the treatment of various other environmental pollutants as well.

NaFeS2 as a new photocatalytic material for the degradation of industrial dyes

By employing a simple hydrothermal process, a new class of ternary alkali metal-based chalcogenide (NaFeS2 (NFS)) has been produced and anchored on to reduced graphene oxide (rGO) sheets for the first time. Transition metal-based chalcogenides (TMC) exhibit limited conductivity because of their semiconducting nature and hence, engineering TMCs with 2D carbonaceous materials yields better catalytic performance. Alkali metal-based chalcogenides and their composites appear to be promising alternatives, whose electrochemical properties haven't been explored much. This work presents a detailed insight into the structure and morphology of the prepared NFS-rGO composite, along with its electrochemical properties. The cyclic voltammetry (CV) response at the NFS-rGO composite electrode for the redox probe K4Fe(CN)6 is better with low peak to peak separation potentials (ΔEp ​= ​99 ​mV) compared to the individual components NFS (ΔEp ​= ​190 ​mV) and GO ( ∆ E p  ​= ​130 ​mV), indicating a better electron transfer kinetics. The NFS-rGO composite electrode displays an enhanced electrocatalytic activity as evidenced by the high electrochemically active surface area (6.09 ​× ​10−2 ​cm2) and the heterogeneous electron transfer rate constant (k0 ​= ​5.4 ​× ​10−2 ​cms−1). In general, the NFS-rGO composite exhibits excellent material as well electrocatalytic properties due to the synergistic effect between NFS and rGO and can further be explored for electrochemical sensing applications as well.

V.G. Dileepkumar

Papers

NaFeS2 as a new photocatalytic material for the degradation of industrial dyes

Ternary alkali metal chalcogenide engineered reduced graphene oxide (rGO) as a new class of composite (NaFeS2-rGO) and its electrochemical performance