CdS nanoparticles have wide applications as photocatalysts for degradation of organic pollutants, but due to their limited turnover number and off-pathway charge recombination processes, their degradation efficiency is low. Herein, aminated graphene quantum dots/CdS (GQDs/CdS) nanobelts were successfully fabricated by solvothermal and hydrothermal processes. The prepared GQDs/CdS were characterized by physical methods to investigate their structure, morphology, optical properties, specific surface area, element composition, and chemical state. GQDs/CdS materials promoted efficient charge separation, and showed high efficiency in the photocatalytic degradation of the organic dye Rhodamine B (RhB) under visible light. The degradation efficiency of RhB samples over 0.05 g of catalysts reached 97.40% after 150 min, a much higher efficiency in comparison to pure CdS. Electron paramagnetic resonance (EPR) spectroscopy provided direct evidence for ˙OH and ˙O₂ ⁻ as the reactive oxidative species using DMPO as a spin trap. Consistent with the experimental results, a possible mechanism of RhB photocatalytic degradation by GQDs/CdS under visible light was proposed. This work may provide environmentally friendly photocatalysts for degrading organic dyes and purifying water.

In this study, the impregnation synthesis of NiO/sepiolite and its application for dye removal during wastewater treatment is introduced. The NiO/sepiolite materials act as an adsorbent/catalyst. It comprises a unique combination of adsorption and high-temperature gas flow regeneration (the NiO/sepiolite acts as a catalyst at this stage, using regeneration rate as evaluation index of catalytic activity of NiO/sepiolite) in a single unit, in which the NiO/sepiolite was regenerated and reused for the next round adsorption of dye. An aqueous solution of methylene blue was used to evaluate the adsorption and regeneration performance of the adsorbent/catalyst. The regeneration rate reached 74% when the reaction time and temperature were 7 min and 350 °C, respectively. The effects of the regeneration temperature and volume fraction of O₂ on the regeneration rate were investigated. And the regeneration reaction kinetics was provided. The combination of adsorptive and catalytic properties in the NiO/sepiolite composites received interesting results for removing refractory biodegradable organic pollutants. This work provides new insights for the removal of dye from wastewater using Ni catalysts supported on natural low-cost clay.

Pharmaceutical wastewater underwent treatment through a combined process involving adsorption and biodegradation.

A novel and highly efficient wastewater treatment process for the removal of industrial dyes was proposed in this study. The method involved the regeneration of Ce–Ni/sepiolite, which acted as an adsorbent/catalyst, exhausted with the cationic dye auramine O (AO)—a frequently-used industrial dye—under a stream of O₂ hot gas. The Ce–Ni/sepiolite adsorbent/catalyst was successfully synthesized by impregnation and was characterized by XRD, SEM, XPS, and BET techniques. An orthogonal experimental design method was applied to optimize the synthesis conditions of Ce–Ni/sepiolite. These synthesis conditions used the regeneration efficiency/rate of the catalyst as the evaluation index under heated O₂ gas stream regeneration. Ce–Ni/sepiolite exhibited remarkable adsorption and catalytic oxidation degradation qualities for AO. The regeneration rate of as-prepared Ce–Ni/sepiolite reached 112.9% after 1 hour at 500 °C under 6 L min⁻¹ of hot gas. The batch adsorption capacities were found to be 210.60 mg g⁻¹ (25 °C), 243.90 mg g⁻¹ (35 °C) and 263.16 mg g⁻¹ (45 °C). 45 °C seemed to allow for the optimum adsorption capacity. Ce–Ni/sepiolite also showed high dynamic adsorption capacity, able to treat 48 bed volume (BV) of the dye solution with a residual concentration of 0 mg L⁻¹ when the height to diameter ratio is 2.5. The adsorption and regeneration mechanisms were proposed. The as-synthesized Ce–Ni/sepiolite can be used as an efficient adsorbent and catalyst in wastewater treatments. This further supports the prospective usability of the sepiolite adsorbent for dye removal in future industrial applications.