Immobilization of TiO₂ Nanoparticles on Chlorella pyrenoidosa Cells for Enhanced Visible-Light-Driven Photocatalysis

A swarm of helical photocatalysts with controlled catalytic inhibition and acceleration by magneto-optical stimuli

Highly persistent and toxic organic pollutants increasingly accumulate in freshwater resources, exacerbating the human water scarcity crisis. Developing novel microrobots with high catalytic performance, high mobility, and recycling capability integrated to harness energy from the surrounding environment to degrade pollutants effectively remains a challenge. Here, we report a kind of Spirulina (SP)-based magnetic photocatalytic microrobots with a substantially decreased band gap than that of pure photocatalysts, facilitating the generation of stable holes and electrons. Under sunlight irradiation, the degradation rate of rhodamine B (RhB) by the microrobots could be increased by 7.85 times compared with that of pure BiOCl, indicating its excellent photocatalytic performance. In addition, the microrobots can swarm in a highly controllable manner to the targeted regions and perform selective catalytic degradation of organic pollutants in specific areas by coupling effect of light and magnetic field. Importantly, the catalytic capability of the swarming microrobots can be activated by light stimulus whereas inhibited by magneto-optical stimuli, with a rate constant 2.15 times lower than that of pure light stimulation. The biohybrid and magneto-optical responsive microrobots offer a potential platform for selective pollutants catalysis at assigned regions in wastewater treatment plants.

A novel polyaniline/NiO nanocomposite as a UV and visible-light photocatalyst for complete degradation of the model dyes and the real textile wastewater

The textile processing industry utilizes enormous amounts of water. After the dying process, the wastewater discharged to the environment contains carcinogens, non-biodegradable, toxic, and colored organic materials. This study aimed to develop a nanocomposite material with improved photocatalytic activity to degrade textile dyes and without a need for a post-separation process after the use. For this, nickel oxide nanoparticles (NiO NPs) were synthesized by a simple method in aqueous media. Then, NiO-doped polyaniline (PANI/NiO) with efficient absorption in the visible region (optical band gap of 2.08 eV) synthesized on a stainless steel substrate with electropolymerization of aniline in the aqueous media. The photocatalytic activity of PANI/NiO film was also investigated by the degradation of model dyes. Under UV and visible light irradiation, the PANI/NiO film degraded methylene blue and rhodamine B dyes entirely in 30 min. Moreover, the PANI/NiO film was also utilized to degrade real textile wastewater (RTW) without applying any pre-process; it was entirely decomposed by the nanocomposite film in only 45 min under UV light irradiation. The photocatalytic reaction rate of the pure PANI film is increased as 2.5 and 1.5 times with the addition of NiO NPs under UV and visible light irradiations for degradation RTW, respectively. The photocatalytic efficiency was attributed to reduced electron-hole pair recombination on the photocatalyst surface. Furthermore, the photocatalytic stability is discussed based on re-use experiments. The photocatalytic performance remains nearly unchanged, and the degradation of dyes is kept 94% after five cycles.

Investigation on Characteristics of Microwave Treatment of Organic Matter in Municipal Dewatered Sludge

This study aimed to utilize a microwave technology to degrade active organic matters of the municipal dewatered sludge in a high-temperature environment. The effects of extraction agent, nanomaterial assistants, and microwave-absorbing agents and activating agents on the degradation efficiency were investigated. Dimethyl carbonate was used as the extraction agent. Nanostructured titanium oxide (TiO2) and zinc oxide (ZnO) exhibited effective assistance in the process of microwave treatment. We also developed a kind of microwave-absorbing agent, which was the sludge-based biological carbon. The sodium sulfate (Na2SO4), calcium hydroxide (Ca(OH)2), and magnesium chloride (MgCl2) were selected as activating agents to facilitate the organic matter discharging from the sludge. Through optimizing the experimental factors, it was confirmed that 0.1 wt% TiO2, 0.1 wt% ZnO, 2 wt% dimethyl carbonate, 10 wt% sludge-based biological carbon, 7.5 wt% Ca(OH)2, 0.5 wt% MgCl2, and 6 wt% Na2SO4 were the most appropriate addition amounts in the municipal dewatered sludge to make the organic matter decrease from 42.17% to 22.45%, and the moisture content reduce from 82.98% to 0.48% after the microwave treatment. By comparison, the organic matter degradation is almost zero, and the moisture content decreases to 8.69% without any additives. Moreover, the residual inert organic matter and sludge can be further solidified to lightweight construction materials by using liquid sodium silicate as the curing agent. The research provides a significant reference for the effective, fast, and low-cost treatment of the organic matter in the municipal sludge.