Visible light degradation of reactive black-42 by novel Sr/Ag-TiO2@g-C3N4 photocatalyst: RSM optimization, reaction kinetics and pathways

In situ formation of 2-thiobarbituric acid incorporated g-C3N4 for enhanced visible-light-driven photocatalytic performance

Embedding heterocycles into the skeleton of g-C₃N₄ has been proved to be a simple and efficient strategy for improving light response and the separation of photo-excited charges. Herein, 2-thiobarbituric acid incorporated g-C₃N₄ (TBA/CN) with good photocatalytic efficiency for Rh B degradation and H₂ production was successfully achieved via a facile thermal copolymerization approach. The incorporation of aromatics and S atoms into the skeleton of g-C₃N₄ was identified via systematic characterizations. This unique structure contributed to the narrowed band-gap, extended delocalization of lone pair electrons and changed electron transition pathway, which led to the enhanced visible light utilization, accelerated charge migration and prolonged electron lifetime, subsequently resulting in the significant boost of photocatalytic activity. The optimal TBA/CN-3 sample yielded the largest Rh B degradation rate constant k value of 0.0273 min⁻¹ and simultaneously highest rate of H₂ evolution of 0.438 mmol g⁻¹ h⁻¹, which were almost 3.5 and 3.8 folds as fast as that of the pristine CN, respectively. Finally, the photocatalytic mechanism was proposed for the detailed elucidation of the process of Rh B degradation coupled with H₂ production.

Embedding heterocycles into the skeleton of g-C₃N₄ has been proved to be a simple and efficient strategy for improving light response and the separation of photo-excited charges.

Optimization of pretreatment in pymetrozine production wastewater via reactive distillation and side-stream distillation methods with response surface methodology

Lots of highly concentrated saline organic wastewater is produced during the pymetrozine production process, causing environmental pollution and waste of resources if discharged directly. Research on actual pymetrozine wastewater treatment is quite scarce. Existing treatment methods of pesticide wastewater usually have disadvantages of long treatment time, low processing efficiency and low recovery rate. To solve these problems, a pretreatment process for pymetrozine wastewater was studied based on material recovery and pollutant degradation. The ammonia conversion process was experimentally investigated by reactive distillation. The reaction product vapor was neutralized and then separated by side-stream distillation. Aspen Plus and response surface methodology were employed to simulate and optimize the operating conditions. Box-Behnken design was used to investigate the individual and interaction effects on methanol purification and sodium acetate removal. Experimental study was carried out on the basis of theoretical simulation data. The result showed that the optimized methanol content on tower top was 99.28% with a yield of 99.95% and methanol content of side withdrawal was 0.01%. The process can be applied for pesticide wastewater treatment to recycle high purity chemical materials, and meets the national sewage comprehensive emission standard.

KOH-Activated Geopolymer Microspheres Recycle Co(II) with Higher Adsorption Capacity than NaOH-Activated Ones

A new type of absorbent with high efficiency was synthesized by KOH-activated slag-based geopolymer microspheres (K-SGM), which exhibited higher adsorption capacities for recycling Co(II) (Q _e,K-SGM = 192.31 mg/g, Q _e,Na-SGM = 91.21 mg/g) than NaOH-activated ones (Na-SGM). During the Co(II) adsorption process, these two kinds of geopolymeric adsorbents could be combined with heavy metal ions to optimize each other and form heavy metal-grown aid adsorbents. The morphology of Na-SGM and K-SGM was different which varied from coarse pores to nanonetwork or nanosheets after Co(II) adsorption, and the Brunauer-Emmett-Teller (BET) surface areas of Na-SGM (10.46 m²/g) and K-SGM (22.96 m²/g) increased to 117.38 and 228.73 m²/g after Co(II) adsorption, respectively. The BET surface area of K-SGM is twice that of Na-SGM whether before or after Co(II) ion adsorption. The hydrated ionic radius of K and Na, the alkalinity degree of K⁺ and Na⁺, the electronegativity of Na-SGM and K-SGM surface, the BET surface area and Fourier transform infrared changes of CO₃ ^2- and OH before and after Co(II) adsorption, and X-ray photoelectron spectroscopy analysis like the relative content of geopolymer gel and bridging oxygen bonds in the Na-SGM and K-SGM are the fundamental reasons for the obvious differences in Co(II) adsorption between Na-SGM and K-SGM.