Rajesh Jagannath Tayade

P–N junction photocatalysts have emerged as versatile and efficient semiconductor materials for solar-driven environmental and energy applications due to their intrinsic ability to promote directional charge separation via a built-in electric field. This review provides a comprehensive overview of the fundamental principles governing P–N junction formation, including band alignment, Fermi-level equilibration, and interfacial charge-transfer mechanisms, and correlates these features with photocatalytic performance. Particular emphasis is placed on the role of the internal electric field in suppressing electron–hole pair recombination and enabling spatial separation of redox reactions. The applications of P–N junction photocatalysts are systematically discussed across environmental pollutant remediation, energy conversion, air purification, and antibacterial activity. In pollutant degradation systems, P–N systems exhibit dual degradation mechanisms, employing an electron-driven reduction process for heavy-metal removal and reactive-oxygen-species-mediated oxidation pathways for the degradation of nonheavy-metal pollutants, such as dyes, pharmaceuticals, and pesticides. For energy applications, the review examines photocatalytic hydrogen (H2) evolution and CO2 reduction, emphasizing the importance of band structure engineering and multielectron transfer pathways in determining activity and product selectivity. Air purification and antimicrobial applications further demonstrate the effectiveness of P–N junctions in generating sustained oxidative species for degradation of gaseous pollutants and pathogen inactivation. A comparative mechanistic framework is presented to unify these diverse applications, illustrating how charge-carrier dynamics dictate reaction pathways. Finally, key challenges, including interfacial control, stability, and scalability, are critically evaluated, and future research directions focusing on advanced material design, in situ characterization, field implementation of P–N junction photocatalysts, and their potential application in sustainable environmental and energy technologies are proposed.

Titanium dioxide (TiO₂) is one of the stable and potential metal oxide semiconductor nanomaterials with flexible properties which allows them to be used in a variety of applications (i.e., environmental remediation, energy storage and production, and also as a pigment in personal care products, etc.). However, its low surface area, poor adsorption capacity and high bandgap energy (~3.2 eV) prevents its full potency. Especially, TiO₂ with high bandgap (~3.2 eV) reduces its visible light absorption capacity and catalytic efficiency. Various modification processes (i.e., metal and non-metal doping, composite materials (mixed metal oxide, high surface area adsorbents), and dye sensitization etc.) have been accomplished for stimulating the characteristics of TiO₂ and the associated catalytic efficiency. Among the modifications, the non-metal doping process in TiO₂, specifically nitrogen doping, is one of the efficient dopants for enhancing the photocatalytic efficiency of TiO₂ in the presence of visible light irradiation. However, the morphology of TiO₂, structural changes in TiO₂ during N-doping, properties (e.g., morphology and electronic) of N-doped TiO₂ and also reaction operational parameters (e.g., doping concentration) hold a greater impact for enhancing the photocatalytic properties of TiO₂ either positively or negatively. Furthermore, the synthesis methodologies have a major influence on the synthesis of stable N-TiO₂ with pronounced photocatalytic efficiencies. Nevertheless, the methodologies for highly stable N-TiO₂ synthesis, properties evaluation and their correlation with photocatalytic efficiencies are still not appropriately stabilized to accomplish the commercial utilization of N-TiO₂. Therefore, this review article focuses on the synopsis of various synthesis methodologies and either their efficiencies or inefficiencies, the mechanism involved in the doping processes, changes in the structural, electronic and morphological properties observed due to the N-doping along with the photocatalytic capacity. Furthermore, the opportunities, challenges and future requirements linked to the development of durable N-doped TiO₂-based semiconductor nanomaterials for efficient catalytic performance is also represented.

The present study demonstrates the BiVO₄ nanoparticles synthesized by co-precipitation (CPM), hydrothermal (HTM) and solution combustion method (SCM) and their visible light photocatalytic activity under irradiation of green light emitting diodes. The synthesized catalysts were characterized by Powder X-ray Diffraction, UV-vis Diffuse reflectance spectroscopy, BET Surface area analysis, Fourier Transform Infrared spectroscopy and Scanning electron microscopy. Result demonstrated that the photocatalytic activity of BiVO₄ catalyst synthesized by solution combustion method has 4.7, 1.9 and 6.7 times higher photocatalytic activity under irradiation of green light emitting diodes as compared to ultraviolet, blue and red light emitting diodes respectively. It has also been found that the photocatalytic activity of the synthesized BiVO₄ by SCM is 6.5 times more as compared to commercial TiO2 under green light emitting diodes irradiation. Furthermore, the room temperature fluorescence and quenching analysis was carried out for the determination of hydroxyl radical generation and understanding photocatalytic activity of the catalyst under green light emitting diodes irradiation. Additionally, the effect of operational parameters under irradiation of green light emitting diodes was studied to optimize catalyst amount, pH, initial dye concentration and amount of H2O2. Recyclability study concern about solution combustion synthesized BiVO₄ catalyst has also been done up to 5 cycles in presence of green light emitting diodes irradiation.