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In this paper, tartaric acid (C[sub.4]H[sub.6]O[sub.6]) was used as a reductant to treat chromium (VI)-containing solution. Several independent experimental parameters, including reaction temperature, concentration of H[sub.2]SO[sub.4], concentration of C[sub.4]H[sub.6]O[sub.6] and reaction time, on the reduction process were studied. The results showed that 100% of the Cr (VI) could be reduced by C[sub.4]H[sub.6]O[sub.6] in a strong acidic environment under a high reaction temperature. All of the experimental parameters showed positive effects on the reduction process and followed the order [H[sub.2]SO[sub.4]] > [C[sub.4]H[sub.6]O[sub.6]] > reaction temperature > reaction time. A higher concentration of tartaric acid and higher reaction temperature could facilitate the reduction process and reduce reaction time.

In this study, nitrogen-doped TiO[sub.2] heterojunction materials were successfully synthesized via a facile one-step solvothermal approach. A range of advanced characterization techniques were employed to thoroughly analyze the structural and compositional properties of the synthesized photocatalysts, and their application potential for tetracycline (TC) degradation under visible light was studied. The results indicated that N-doped TiO[sub.2] exhibited a well-defined hierarchical micro/nanostructure and formed an efficient anatase/rutile homogeneous heterojunction. The photocatalytic performance of N-TiO[sub.2] for TC degradation under visible light was significantly enhanced, achieving a degradation efficiency of up to 87% after 60 min of irradiation. This improvement could be attributed to the synergistic effects of optimal nitrogen doping, heterojunction formation, and the hierarchical micro/nanostructure, which collectively reduced the bandgap energy and suppressed the recombination rate of photogenerated carriers. Furthermore, density functional theory (DFT) calculations were conducted to systematically explore the impacts of substitutional and interstitial nitrogen doping on the energy band structure of TiO[sub.2].

Ceramic samples of CuCr[sub.1−x]Y[sub.x]O[sub.2] (x = 0–0.02) were synthesized via the high temperature solid-state reaction method, and the influence of Y[sup.3+] doping on their microstructure and antiferromagnetic phase transitions was systematically investigated. Y[sup.3+] doping increased the unit cell volume from 130.928 Å[sup.3] for x = 0 to 131.147 Å[sup.3] for x = 0.0200, and the average grain size decreased from 3.38 μm for x = 0 to 4.27 μm for x = 0.0200. The Cr and Y elements maintained +3 valence, while the Cu element had +1 valence. All samples showed obvious paramagnetism when the temperature was higher than 140 K. When the temperature continued to decrease, the lattice expansion changed the bond length and bond angle of the Cr-O-Cr bond, resulting in a change in the superexchange interaction, and the magnetic susceptibility increased significantly, gradually showing antiferromagnetism. The T[sub.N] of the undoped sample was about 46 K, the T[sub.N] of the doped sample with x = 0.0175 was about 21 K, and the T[sub.N] of other doped samples was about 30 K. This result indicates that Y[sup.3+] doping enhanced the antiferromagnetism of the sample but also weakened its antiferromagnetic stability.

In this study, a novel composite DUT-5/Bi.sub.2MoO.sub.6 (DUT-5/BMO) photocatalytic material was prepared by two-step hydrothermal method for the first time. The materials were characterized by SEM, XPS, etc. Studies have shown that material with a new n-n heterojunction structure can quickly degrade tetracycline. DUT-5 was embedded between the Bi.sub.2MoO.sub.6 nanosheets, which promotes the photogenerated electrons from DUT-5 flows to Bi.sub.2MoO.sub.6, thereby reducing the recombination rate of photo-generated electron-hole pairs. The BET results show that the composite material has a larger specific surface area than the monomer Bi.sub.2MoO.sub.6. It can provide more active sites. After 60 min of visible light irradiation, the photocatalytic degradation efficiency of TC with 15% DUT-5/BMO reached 84.22%, which is 5.37 and 2.12 times higher than that of pure DUT-5 and Bi.sub.2MoO.sub.6, ·O.sub.2.sup.- and h.sup.+ were the main active substances in the photocatalysis process. In addition, DUT-5/BMO composites show excellent stability and recyclability in 5 times cyclic experiments. In conclusion, DUT-5/BMO has good stability in the environment, and can be used for environmental remediation without pollution. Graphical

In this study, a novel composite DUT-5/Bi.sub.2MoO.sub.6 (DUT-5/BMO) photocatalytic material was prepared by two-step hydrothermal method for the first time. The materials were characterized by SEM, XPS, etc. Studies have shown that material with a new n-n heterojunction structure can quickly degrade tetracycline. DUT-5 was embedded between the Bi.sub.2MoO.sub.6 nanosheets, which promotes the photogenerated electrons from DUT-5 flows to Bi.sub.2MoO.sub.6, thereby reducing the recombination rate of photo-generated electron-hole pairs. The BET results show that the composite material has a larger specific surface area than the monomer Bi.sub.2MoO.sub.6. It can provide more active sites. After 60 min of visible light irradiation, the photocatalytic degradation efficiency of TC with 15% DUT-5/BMO reached 84.22%, which is 5.37 and 2.12 times higher than that of pure DUT-5 and Bi.sub.2MoO.sub.6, ·O.sub.2.sup.- and h.sup.+ were the main active substances in the photocatalysis process. In addition, DUT-5/BMO composites show excellent stability and recyclability in 5 times cyclic experiments. In conclusion, DUT-5/BMO has good stability in the environment, and can be used for environmental remediation without pollution.

In this study, a Z-Scheme WO[sub.3]/CoO p-n heterojunction with a 0D/3D structure was designed and prepared via a simple solvothermal approach to remove the combined pollution of tetracycline and heavy metal Cr(VI) in water. The 0D WO[sub.3] nanoparticles adhered to the surface of the 3D octahedral CoO to facilitate the construction of Z-scheme p-n heterojunctions, which could avoid the deactivation of the monomeric material due to agglomeration, extend the optical response range, and separate the photogenerated electronhole pairs. The degradation efficiency of mixed pollutants after a 70 min reaction was significantly higher than that of monomeric TC and Cr(VI). Among them, a 70% WO[sub.3]/CoO heterojunction had the best photocatalytic degradation effect on the mixture of TC and Cr(VI) pollutants, and the removing rate was 95.35% and 70.2%, respectively. Meanwhile, after five cycles, the removal rate of the mixed pollutants by the 70% WO[sub.3]/CoO remained almost unchanged, indicating that the Z-scheme WO[sub.3]/CoO p-n heterojunction has good stability. In addition, for an active component capture experiment, ESR and LC-MS were employed to reveal the possible Z-scheme pathway under the built-in electric field of the p-n heterojunction and photocatalytic removing mechanism of TC and Cr(VI). These results offer a promising idea for the treatment of the combined pollution of antibiotics and heavy metals by a Z-scheme WO[sub.3]/CoO p-n heterojunction photocatalyst, and have broad application prospects: boosted tetracycline and Cr(VI) simultaneous cleanup over a Z-scheme WO[sub.3]/CoO p-n heterojunction with a 0D/3D structure under visible light.

In this work, a novel S-scheme Bi.sub.2WO.sub.6@NH.sub.2-MIL-125(Ti) heterojunction composite was synthesized for the first time by a secondary hydrothermal method. XRD, SEM, TEM, XPS and DRS were used to characterize the Bi.sub.2WO.sub.6@NH.sub.2-MIL-125 (Ti) composite. The results show that NH.sub.2-MIL-125(Ti) is embedded between Bi.sub.2WO.sub.6 nanosheets, the composite materials have narrower bandgap and enhanced absorption of visible light. The recombination tendency of electron-hole pairs were also weakened by the S-scheme heterojunction between the two monomers. The best content of NH.sub.2-MIL-125(Ti) was 13 wt%, the degradation rate of RhB reached 98% in 50 min, which was 5 times and 18 times that of the Bi.sub.2WO.sub.6 and NH.sub.2-MIL-125 (Ti) respectively. After several cycles under visible light, the composite materials still have good degradation rate and excellent stability, indicating that these composite materials have great development potential in the environmental field. Graphic

In this work, a novel S-scheme Bi.sub.2WO.sub.6@NH.sub.2-MIL-125(Ti) heterojunction composite was synthesized for the first time by a secondary hydrothermal method. XRD, SEM, TEM, XPS and DRS were used to characterize the Bi.sub.2WO.sub.6@NH.sub.2-MIL-125 (Ti) composite. The results show that NH.sub.2-MIL-125(Ti) is embedded between Bi.sub.2WO.sub.6 nanosheets, the composite materials have narrower bandgap and enhanced absorption of visible light. The recombination tendency of electron-hole pairs were also weakened by the S-scheme heterojunction between the two monomers. The best content of NH.sub.2-MIL-125(Ti) was 13 wt%, the degradation rate of RhB reached 98% in 50 min, which was 5 times and 18 times that of the Bi.sub.2WO.sub.6 and NH.sub.2-MIL-125 (Ti) respectively. After several cycles under visible light, the composite materials still have good degradation rate and excellent stability, indicating that these composite materials have great development potential in the environmental field.

Photocatalytic technology, which is regarded as a green route to transform solar energy into chemical fuels, plays an important role in the fields of energy and environmental protection. An emerging S-scheme heterojunction with the tightly coupled interface, whose photocatalytic efficiency exceeds those of conventional type II and Z-scheme photocatalysts, has received much attention due to its rapid charge carrier separation and strong redox capacity. This review provides a systematic description of S-scheme heterojunction in the photocatalysis, including its development, reaction mechanisms, preparation, and characterization methods. In addition, S-scheme photocatalysts for CO[sub.2] reduction are described in detail by categorizing them as 0D/1D, 0D/2D, 0D/3D, 2D/2D, and 2D/3D. Finally, some defects of S-scheme heterojunctions are pointed out, and the future development of S-scheme heterojunctions is proposed.