This work focuses on the synthesis of undoped and doped lanthanum oxide nanoparticles (La2O3 NPs) by a simple co-precipitation method for the catalytic reduction of 4-nitrophenol (4-NP) using NaBH4 as a reducing agent. Their optical properties, morphologies, structure, chemical compositions and electronic properties were carefully characterized by XRD, FTIR, SEM, TEM, PL and UV–visible absorption spectroscopy. The SEM and TEM images showed various shape morphologies and sizes of the particles. The XRD pattern revealed a polycrystalline nature with the hexagonal structure of the La2O3 NPs. The synthesized undoped and doped La2O3 NPs were also employed as catalysts for the reduction of 4-nitrophenol, it shows that the doped (Sm3+, Gd3+ and Hf3+) La2O3 NPs provided better catalytic activity than the undoped La2O3 NPs. Moreover, Hf3+ doped La2O3 NPs exhibited an enhanced catalytic activity for the reduction of 4-nitrophenol to 4-aminophenol in 90 min. The catalytic conversion was studied by UV–vis spectroscopy with high reduction rate (k = 2.048 min−1). The applications of the present study may utilize in the removal of toxic pollutants in a cleaning of environmental pollution as well as in industrial applications.

The construction of ternary semiconductor nanostructures has attracted much attention in photocatalysis by virtue of their tunable elemental composition and band structure. Here, ternary semiconductor Zn_xAg_1−xS (0 ≤ x ≤ 1) composites were successfully prepared by a simple and low-cost hydrothermal method without using any surfactant. Combined analyses using XRD, N₂ sorption, SEM, TEM and UV-vis DRS revealed that the ternary composite semiconductor materials exhibited well-developed crystalline frameworks, large surface areas of 15–70 m² g⁻¹, sizes of 10–30 nm, and outstanding UV light absorption properties. Data from XRD and TEM indicate that photocatalysis might contribute to the formation of the strong interfacial interaction between ZnS and Ag₂S nanoparticles. The photocatalytic activities were investigated via the degradation of organophosphorus pesticides, including malathion (MLT), monocrotophos (MCP) and chlorpyrifos (CPS), using the Zn_xAg_1−xS composites under UV light irradiation. The toxicity of MLT, MCP, and CPS was reduced by photocatalysis and photolysis; however, photocatalysis had a greater impact. Superior photocatalytic performance was exhibited by the Zn_0.5Ag_0.5S catalyst owing to its large surface area and the presence of Ag⁰ with improved charge transfer in comparison with that of bare ZnS and Ag₂S. Assays of stability and reusability indicated that the Zn_0.5Ag_0.5S composite retained more than 85% of its activity after five cycles of use. On the basis of the results, a possible photocatalytic mechanism of the prepared samples was proposed. This study indicates a potential application of the ternary semiconductor materials in the efficient UV light-driven photocatalytic degradation of other pollutants that may cause environmental pollution.

The fabrication of g-C₃N₄nanosheet-based sensing platforms for the detection or removal of heavy toxic metal ions from wastewater has a great interest due to their unique properties and these are carcinogenic and lead to serious health concerns.

In this work, we report a stable g-C₃N₄, Bi₂S₃, and g-C₃N₄/Bi₂S₃ composite catalysts were prepared via a facile one-pot microwave-assisted method and characterized. The orthorhombic phase and nearly spherical shape of the particles with an average diameter of 5–25 nm of g-C₃N₄/Bi₂S₃ composite were obtained from XRD and TEM. The composite also exhibits a high surface area (32.15 m²/g), which may provide convenient transportation and diffusion for substrate molecule. The optical studies were displayed the g-C₃N₄/Bi₂S₃ composite has a sharp absorption band in the visible region, higher charge separation, and reduced recombination rate. These results show that the Bi₂S₃ NPs have good crystallinity and are uniformly deposited on the surface of the g-C₃N₄ sheet. The catalytic performance of the g-C₃N₄/Bi₂S₃ composite for the reduction of 4-NP to 4-AP was exhibited approximately 100%, which is 1.48 and 2.34 times higher than the Bi₂S₃ and g-C₃N₄ catalysts, respectively. The pseudo-first-order rate constant was estimated as 1.648 × 10 ⁻² min⁻¹ for the reduction of 4-NP using g-C₃N₄/Bi₂S₃ composite in 1 h reaction time. The effect of catalyst dosage (0–30 mg) was also investigated for the reduction of 4-NP using g-C₃N₄/Bi₂S₃ composite catalyst. Moreover, the reusability of the g-C₃N₄/Bi₂S₃ composite was exhibited a better reduction of the 4-NP even after 5 cycles and it was found that 8% reduction in the initial reduction rate. The obtained results from this study show that g-C₃N₄/Bi₂S₃ composite has the potential efficiency and stability to make it an ideal catalyst for the reduction of toxic effluents and wastewater treatment. GRAPHICAL ABSTRACT

The g-C₃N₄ nanosheets, CdS NPs, and g-C₃N₄/CdS composite were fabricated using sonochemical method for the efficient photocatalytic degradation of CV dye, MCP pesticide and catalytic reduction of 4-NP using NaBH₄ as a reducing agent. The synthesized nanocatalysts were characterized by various physicochemical techniques. The g-C₃N₄/CdS composite was capably degradation of CV and MCP, and catalyze the reduction of 4-NP to 4-AP in the presence of NaBH₄ very efficiently with good recyclability up to five cycles than g-C₃N₄ and CdS NPs. Further, the temperature effect on the catalytic reduction of 4-NP using g-C₃N₄/CdS composites was also studied. The catalytic reduction reaction follows the pseudo-first-order kinetics. The corresponding rate constants increased with the temperature, revealing activation energy of 26.42 kJ/mol. The scavenging radicals from the antioxidant activity of the synthesized composites were determined by DPPH method. In addition, the synthesized composites showed good antibacterial and antifungal activities using paper disc method.