Synthesis of nitrogen-doped carbon nanotubes-FePO4 composite from phosphate residue and its application as effective Fenton-like catalyst for dye degradation.

Phosphate residue is regarded as a hazardous waste, which could potentially create significant environmental and health problems if it is not properly treated and disposed of. In this study, nitrogen-doped carbon nanotubes-FePO4 (NCNTs-FePO4) composite was successfully synthesized from phosphate residue, and its application as an effective catalyst was explored. Firstly, an effective method was developed to recover FePO4 from phosphate residue, achieving an impressive FePO4 mass recovery rate of 98.14%. Then, the NCNTs-FePO4 catalyst was synthesized from the recovered FePO4 by two main reactions, including surface modification and chemical vapor deposition. Finally, the synthesized NCNTs-FePO4 was applied to photo-degrade 15 mg/L Rhodamine B (RhB) in a Fenton-like system. The results showed that 98.9% of RhB could be degraded in 60 min, closely following the pseudo-first-order kinetics model. It was found that even after six consecutive cycles, NCNTs-FePO4 still retained a high catalytic capacity (>50%). Moreover, •OH radicals participating in the RhB degradation process were evidenced using quenching experiments and electron paramagnetic resonance analysis, and a rational mechanism was proposed. It was demonstrated that the materials synthesized from hazardous phosphate residue can be used as an effective catalyst for dye removal.

Modified iron phosphate/polyvinyl alcohol composite film for controlled-release fertilisers.

Traditional soluble phosphorous (P) fertilisers can be easily leached to pollute water systems, resulting in water eutrophication, a major environmental problem from the oversupply of unused nutrients. One innovative solution is to control the release of P upon demands of the plants. This study established a new concept of controlled-release P fertiliser via incorporation of ferric phosphate (FePO4) as a P source in polyvinyl alcohol (PVA) films, which can immobilise the FePO4 particles and stimuli-responsively accelerate their release rate in the presence of citric acid. More importantly, FePO4 used in this work originated from steelmaking slag as a potential waste reuse. Due to the low solubility of FePO4, diethylamine was introduced to modify FePO4 particles to facilitate the release of P before incorporating with PVA. The effects of diethylamine modification and the properties of FePO4/PVA films were systematically investigated through microscopic and spectroscopic methods. The release of P from particles and films was examined in both deionised water and citric acid solution for 30 days. The results showed a tenfold increase of the release rate of modified FePO4/PVA in citric acid solution compared with that in deionised water, and also a doubled release rate of the modified FePO4/PVA compared to that of FePO4/PVA in citric acid. The improved performance suggests that PVA can maintain the phosphorous content with exposure to water and expedite release in citric acid upon the demand of plants. This composite film offers a new opportunity for the application of insoluble phosphate as a phosphorous fertiliser.

[Direct photolysis of methylamine gas by KrBr* excilamp].

A study on methylamine (MA) photo-dissociation in gas phase has been carried out using UV radiation from a 207 nm KrBr* excilamp driven by a sinusoidal electronic control gear. The influence factors including gas flow rate, initial concentration and input power of removal efficiency were investigated. The radiant power and spectrum of the lamp were measured. Several parameters were investigated including removal efficiency, energy yield, carbon balance and CO2 selectivity in order to comprehensively evaluate the photo-dissociation process. It was shown that the removal efficiency increased with enhanced input power, decreased gas flow rate and increased MA initial concentration. Energy yield had positive pertinence with MA initial concentration, and it would obtain optimal value at 65.1 W. Carbon balance and CO2 selectivity showed slighter enhancement when lamp power increased and gas flow rate declined. The removal efficiency of 56.8% was achieved at a lamp power of 79.8 W, a gas flow rate of 9.0 m3 x h(-1) and an MA initial concentration of 2 897 mg x m(-3). Under the above mentioned experimental conditions, energy yield reached 185.6 g (kW x h)(-1), and carbon balance and CO2 selectivity were 16.8% and 10.3%, respectively. At last, secondary products formed were analyzed by gas chromatography-mass spectrometry and the photo-degradation mechanism of MA was suggested on the basis of UV-vis absorption spectrum.