Wastewater generation and treatment is an ever-increasing concern in the current century due to increased urbanization and industrialization. To tackle the situation of increasing environmental hazards, numerous wastewater treatment approaches are used—i.e., physical, chemical, and biological (primary to tertiary treatment) methods. Various treatment techniques being used have the risks of producing secondary pollutants. The most promising technique is the use of different materials as adsorbents that have a higher efficacy in treating wastewater, with a minimal production of secondary pollutants. Biosorption is a key process that is highly efficient and cost-effective. This method majorly uses the adsorption process/mechanism for toxicant removal from wastewater. This review elaborates the major agricultural and non-agricultural materials-based sorbents that have been used with their possible mechanisms of pollutant removal. Moreover, this creates a better understanding of how the efficacy of these sorbents can be enhanced by modification or treatments with other substances. This review also explains the re-usability and mechanisms of the used adsorbents and/or their disposal in a safe and environmentally friendly way, along with highlighting the major research gaps and potential future research directions. Additionally, the cost benefit ratio of adsorbents is elucidated.

In the present work, TiO₂/g-C₃N₄ nanocomposites were synthesized by using highly crystalline TiO₂ nanorods/rice (NRs) and various percentages of g-C₃N₄ via a facile, scalable, and inexpensive pyrolysis method. The synthesized nanocomposites were characterized by various techniques, e.g., X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), N₂ adsorption and desorption analysis (BET), Fourier transform infrared spectroscopy (FTIR), UV-vis diffuse reflectance spectroscopy (DRS), electrochemical impedance spectroscopy (EIS), and chronoamperometry (CA). It was found that biodiesel production by the esterification reaction can be remarkably enhanced by coupling TiO₂ with g-C₃N₄; hereby, it was observed that with increasing percentage of g-C₃N₄ from 5 to 10 and 15% with respect to TiO₂ NRs, the photocatalytic activity rose and the maximum photocatalytic activity with 97% conversion was observed for NC-3, i.e., 15% g-C₃N₄/TiO₂. Moreover, the photoactivity of pristine TiO₂ NR aggregates was contrasted with their nanoparticle morphology and was estimated to be slightly better. When applied for photocatalytic Congo red dye degradation, this sample showed a 91% degradation efficiency using only a very small amount of the catalyst. The high catalytic efficiency is attributed to the narrow band gap, exceptionally high surface area, and efficient charge separation properties of the prepared catalysts.