In order to further improve the photocatalytic performance of the SiO₂/TiO₂ composite under visible light irradiation, curcumin-doped SiO₂/TiO₂ nanocomposites were synthesized via directly incorporating it into the structure of SiO₂/TiO₂ during the synthesis using an inexpensive and readily available natural pigment (curcumin) as doping agent. The physicochemical properties of SiO₂/TiO₂ nanocomposites were characterized in detail by X-ray diffraction, transmission electron microscopy, Fourier transform-infrared spectroscopy, N₂ adsorption–desorption isotherms, X-ray photoelectron spectroscopy, and UV-vis diffuse reflectance spectroscopy. The results indicate that all SiO₂/TiO₂ nanocomposites exhibited an anatase phase with a typical mesoporous structure. It was found that the dope of curcumin in the SiO₂/TiO₂ composite could decrease the crystal size, slightly improve the specific surface areas, significantly enhance the visible light absorption, and effectively narrow the band gap energy from 3.04 to 10(eV). Compared with bare SiO₂/TiO₂, the curcumin-doped SiO₂/TiO₂ resulted in enhanced photocatalytic reduction activity for Cr(VI) under visible light irradiation, and the CTS (12) sample with the appropriate content of curcumin of 12 wt % shows the photocatalytic yield reaching 100% within 2.5 hours, which is larger than CT (12) without silica. This could be attributed to the curcumin doping and the synergetic effects of SiO₂ and TiO₂ in SiO₂/TiO₂ nanocomposites.

The design and synthesis of efficient photocatalysts that promote the degradation of organic pollutants in water have attracted extensive attention in recent years. In this work, CdS nanoparticles are grown in situ on Co@C derived from metal–organic frameworks. The resulting hierarchical CdS/Co@C nanostructures are evaluated in terms of their adsorption and photocatalytic ciprofloxacin degradation efficiency under visible-light irradiation. The results show that, apart from offering a large surface area (55.69 m²·g⁻¹), the prepared material can effectively suppress the self-agglomeration of CdS and enhance the absorption of visible light. The CdS/Co@C-7 composite containing 7% wt Co@C has the highest photodegradation rate, and its activity is approximately 4.4 times greater than that of CdS alone. Moreover, this composite exhibits remarkable stability after three successive cycles of photocatalysis. The enhanced photocatalytic performance is largely ascribed to the rapid separation of electron–hole pairs and the effective electron transfer between CdS and Co@C, which is confirmed via electrochemical experiments and photoluminescence spectra. The active substance capture experiment and the electron spin resonance technique show that h⁺ is the main active entity implicated in the degradation of CIP, and accordingly, a possible mechanism of CIP photocatalytic degradation over CdS/Co@C is proposed. In general, this work presents a new perspective on designing novel photocatalysts that promote the degradation of organic pollutants in water.