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Metal-free carbonaceous catalysts are receiving increasing attention in wastewater treatment. Here, nitrogen and sulfur co-doped carbon sphere catalysts (N,S-CSs900-OH) were synthesized using glucose and L -cysteine via a hydrothermal method and high temperature alkali activation. The N,S-CSs900-10%-OH exhibited excellent catalytic performance for the degradation of oxytetracycline (OTC). The degradation rate was 95.9% in 60 min, and the reaction equilibrium rate constant was 0.0735 min−1 (k0–15 min). The synergistic effect of adsorption-promoting degradation was demonstrated in the removal process of OTC. The excellent adsorption capacity of N,S-CSs900-10%-OH ensured the efficient oxidation of OTC. N,S-CSs900-10%-OH reduced the activation energy of the OTC degradation reaction (Ea=18.23 kJ/mol). Moreover, the pyrrolic N, thiophene S and carbon skeleton played an important role in the degradation of OTC based on density function theory, and the catalytic mechanism was expounded through radical and nonradical pathways. The active species involved in the reaction were O2•−, 1O2, SO4•− and •OH, of which O2•− was the primary reactive species. This study provides a new insight into the reaction mechanism for efficient treatment of organic pollutants using metal-free doped porous carbon materials.

Taking advantage of the unique properties of reduced graphene oxide (rGO) and monoclinic crystalline titanium dioxide (TiO2(B)) nanomaterials, a novel rGO–TiO2(B) composite membrane (MrGO–TiO2(B)) was constructed by UV-light-assisted self-assembly of rGO and TiO2 on a nylon membrane. The structure of MrGO–TiO2(B) was characterized by scanning electron microscopy, transmission electron microscopy, UV‐visible diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction analysis. Through 2D/2D self-assembly, rGO and TiO2(B) were more tightly combined, and then MrGO–TiO2(B) exhibited outstanding photocatalytic activity and an excellent methylene blue (MB) removal rate. MB was completely removed in 60 min at a constant rate of 0.042 min−1 by the MrGO–TiO2(B)/H2O2/MB system upon solar simulating Xe lamp irradiation. The synergistic effect of rGO and TiO2(B) facilitated the photocatalytic degradation of MB. TiO2(B) was excited and generated electrons and holes upon irradiation. Some electrons migrated to the surface of TiO2(B) to react with H2O2 to produce hydroxyl radicals ( OH), while the other electrons migrated to the surface of rGO to react with H2O2, producing OH. In addition, a number of superoxide radicals (O2 −) was detected. The holes in the valence band of TiO2(B) directly oxidized MB. The catalytic activity of MrGO–TiO2(B) toward MB degradation remained stable after four rounds of reuse. Therefore, the surface modification of a nylon membrane with TiO2(B) and rGO can serve as a promising route to fabricate photocatalytic membranes for use in the water treatment industry.

With the pollution of perfluoroalkyl substances (PFASs) became increasingly serious, the researches focused on removal of PFASs by adsorption-photocatalysis method has attracted considerable attention. To make the catalyst TiO2 disperse uniformly as quantum dots onto hydrophobic surface which was liable to attract perfluorooctanoic acid (PFOA), the surfactant sodium dodecyl sulfate (SDS) were used in this work, which not only connected the hydrophilic TiCl3 to the hydrophobic sulfonated graphene (SG) nanosheets, but also behaved as the molecular template for controlled nucleation and growth of the nanostructured TiO2. After 3D SG-TiO2 QD nanosheets were fabricated, a series of 3D SG-TiO2 QD aerogels were self-assembled by ice-template. TiO2 uniformly distributed on the surface of SG aerogel at QD size level (2–3 nm) and the size of TiO2 could be effectively regulated by concentration of SDS. Compared with aggregated TiO2 material, 3D SG-TiO2 QD aerogels owned higher adsorption and photocatalytic performance. Benefiting from the hydrophobic surface of 3D SG as well as dispersed TiO2 QDs, 3D SG-TiO2 QD could enrich PFOA instantaneously (0.0381/s) and photocatalytic decomposed them effectively (1.898 E−4/s). PFOA degradation by hole and hydroxyl radicals proceeded via a stepwise mechanism. The column made of 3D SG-TiO2 QD could remove PFOA persistently in cycles of permeation. 3D SG-TiO2 QD possessed powerful adsorption-photocatalytic decomposition capability of PFOA and steady reusability performance. The present work highlights the individual roles and synergistic effect of TiO2 QD and 3D SG for effectively removing PFOA.