Graphical A series of novel MOFs based Bi x Ti y -BTC photocatalysts synthesized by the hydrothermal method for removal of UDMH from wastewater. The interconversion between Ti 3+ and Ti 4+ in Bi 1 Ti 3 -BTC promotes quick electrons transfer. And nano-Fe 3 O 4 prevented agglomeration of Bi 1 Ti 3 -BTC and improved photocatalytic activity, the optimal catalytic degradation performance of 97.02 % was observed at a Bi : Ti molar ratio of 1 : 3. Removal of organic pollutants from wastewater remains a significant challenge. Hence, we report a series of novel MOFs based Bi x Ti y -BTC photocatalysts synthesized by hydrothermal method for decontamination of 1,1-Dimethylhydrazine (UDMH). The preparation parameters of MOFs were optimized, the best catalytic performance was achieved by adjusting the Bi/Ti molar ratio to 1 : 3, with Bi 1 Ti 3 -BTC a photocurrent density of 0.35 mA/cm 2 was reached. The morphology and composition of the materials were analyzed, titanium doping increased the specific surface area. Bi 1 Ti 3 -BTC was loaded with magnetic nano-Fe 3 O 4 , which prevented agglomeration of Bi 1 Ti 3 -BTC and increased the specific surface area, thus improving photocatalytic activity. The band gap structure of the semiconductor materials was estimated by UV-Vis and XPS valence band spectra, while the separation efficiency of photogenerated carriers was investigated by photocurrent density and PL (Photoluminescence) spectrum. The photocatalytic degradation rate of UDMH rapidly decreased after addition of EDTA, indicating that h + was the main active species in the photocatalytic degradation process. The photocatalytic removal efficiency of UDMH with Bi 1 Ti 3 -BTC/Fe 3 O 4 at a concentration of 0.5 g/L reached 97.58 % after illumination for 180 min, and after 210 min near quantitative degradation was observed.
The leakage of unsym-dimethylhydrazine (UDMH) wastewater poses a significant threat to environment due to the enormous toxicity of UDMH and its degradation by-products. The toxicity of UDMH wasterwater is mainly due to the toxicity of nitrogen-containing products. Herein, a microwave-assisted manganese trioxide degradation strategy was proposed based on advanced oxidation process (AOPs). Under recommended reaction conditions of UDMH initial concentration 250 mg/L, initial pH of reaction solution 9, microwave power 300 W, Mn 2 O 3 dosage 10 g/L and reaction duration 1 h, a high COD degradation efficiency of 85.81 %, UDMH degradation efficiency of 99.78 % were achieved. Under this condition, the amount of nitrogen-containing products concerned in the experiment was the least. The effective degradation of UDMH and COD was benifitting from the microwave-accelerated molecular vibration and the abundant active substances catalysed by Mn 2 O 3 , especially •OH. Material characterization results indicated that Mn 2 O 3 might play a catalytic role in reaction. The degradation intermediates of UDMH were further identified by solid-phase microextraction-gas chromatography-mass spectrometry (SPME-GC-MS), and the reaction mechanism was analyzed to reveal possible degradation pathway of UDMH. Under attack of •OH, UDMH degraded into various intermediates. ECOSAR toxicity assessment software analysis and Selenastrum capricornutum toxicity experiment showed that the toxicity of UDMH decreased significantly after microwave assisted Mn 2 O 3 degradation due to the reduction of electrophilic groups. This work provides an effective method to mitigate ecological environmental harm of UMDH wastewater in practical production.
1,1-Dimethylhydrazine (UDMH) and its by-products were considered carcinogenic toxins and represent a serious health hazard to the population once present in water under natural conditions without treatment. The conventional degradation method suffers from incomplete removal of intermediate products (especially N-nitrosodimethylamine (NDMA)), the powdery catalysis being difficult to recover and results in high energy consumption. In this study, a series of Bi2O3/TiO2/Al2O3 (BTA) photocatalysts have been successfully synthesized by a simple dry mixing method with powder material followed by their immobilization. It was evaluated by the photocatalytic degradation of UDMH present in wastewater, which can be recovered by rapid filtration and utilizes only solar energy. The catalyst exhibited markedly enhanced photocatalytic activity for the degradation of UDMH wastewater compared with conventional TiO2/Al2O3 (TA) catalysts under UV, visible and solar irradiation. Besides, the intermediate NDMA was gradually completely degraded. The photocatalysts were extensively characterized using scanning electron microscopy, energy dispersive spectrometry, specific surface area (BET), X-ray diffraction, X-ray photoelectron spectroscopy, UV–visible diffuse reflectance spectroscopy and photo-electrochemical I–t curves evaluation. The results revealed that all the BTA composites exhibited high stability and stronger absorbance in visible light. In addition, the BTA exhibited a reversible photochromic property that can effectively expand the range of light absorption and enhance the photocatalytic activity. The reversible photochromic properties of BTA explained in the proposed mechanism model are expected to be useful for detecting and sensing UDMH or other organic contaminants.
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