Activated carbon/titanium dioxide (AC/TiO₂) nanohybrids were synthesized by a hydrothermal technique using various weight percent of commercial AC and were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Fourier transform infrared (FTIR) and thermogravimetric analysis (TGA). The synthesized nanohybrids were applied to photodegradation of Reactive Red-35 (RR-35) dye in aqueous solution using sunlight. Due to the synergistic effect of adsorption and photodegradation activity, AC/TiO₂ nanohybrids were more efficient in treating the aqueous dye solution than that of AC and TiO₂. The maximum (95%) RR-35 dye removal from the water was obtained with 20 wt% AC/TiO₂ within 30 min at natural pH of 5.6. The possible photodegradation mechanism of RR-35 dye with AC/TiO₂ was discussed from the scavenger test. Moreover, AC/TiO₂ was found to be suitable for long-term repeated applications through recyclability experiments. Therefore, AC/TiO₂ nanohybrid is a promising photocatalyst for treating azo dyes especially RR-35 from water.

A novel B-doped ZnO/TiO₂ (B–ZnO/TiO₂) nanocomposite photocatalyst was prepared using a mechanochemical–calcination method. For the characterization of the synthesized B–ZnO/TiO₂ photocatalyst, XRD, FESEM-EDS, FTIR, UV-Vis DRS, BET, PL, and XPS techniques were used. The bandgap energy of B–ZnO/TiO₂ was reduced, resulting in enhanced visible-light absorption. Significant PL quenching confirmed the reduction in the electron–hole recombination rate. Furthermore, reduced crystallite size and a larger surface area were obtained. Hence, the B–ZnO/TiO₂ photocatalyst exhibited better photocatalytic activity than commercial TiO₂, ZnO, B–ZnO, and ZnO/TiO₂ in the removal of methylene blue (MB) dye under natural sunlight irradiation. The effects of various parameters, such as initial concentration, photocatalyst amount, solution pH, and irradiation time, were studied. Under optimal conditions (MB concentration of 15 mg/L, pH 11, B–ZnO/TiO₂ amount of 30 mg, and 15 min of operation), a maximum MB removal efficiency of ~95% was obtained. A plausible photocatalytic degradation mechanism of MB with B–ZnO/TiO₂ was estimated from the scavenger test, and it was observed that the ${•\mathrm{O}}_2^{-}$ and •OH radicals were potential active species for the MB degradation. Cyclic experiments indicated the high stability and reusability of B–ZnO/TiO₂, which confirmed that it can be an economical and environmentally friendly photocatalyst.

Advanced engineering of naturally occurring materials opens new doors in nanoscience and nanotechnology for the separation and/or removal of environmental hazards. Here, a series of nanocomposites containing kaolinite and chitosan varying in the range of 20 to 80% (w/w) kaolinite were used for the adsorptive removal of a reactive textile dye, Remazol Red, from an aqueous solution. Batch experiments were carried out to investigate the effects of pH, contact time, and initial dye concentration on the adsorption capacity. Nanocomposites containing 80% kaolinite (w/w) and 20% chitosan (w/w), i.e., NK₈₀C₂₀, showed an equilibrium adsorption capacity of 371.8 mg/g at pH 2.5, which was 5.2 times higher than that of commercial activated charcoal. Moreover, NK₈₀C₂₀ was regenerated instantly up to 99.9% at pH 10. Therefore, NK₈₀C₂₀ can be effectively utilized as a potential adsorbent for the separation of Remazol Red and homologous azo dyes from industrial effluents. We expect that the findings from this study will play a vital role in environmental research leading to advanced applications in water purification.