The effects of bismuth (III) doping and ultrathin nanosheets construction on the photocatalytic performance of graphitic carbon nitride for antibiotic degradation.

To further enhance the photocatalytic performance of graphitic carbon nitride (g-C3N4), we rationally combined two strategies (foreign metal doping and ultrathin nanosheet construction) to synthesize bismuth (III) (Bi3+) doped ultrathin g-C3N4 nanosheets (Bi-CNNS) via one-step thermal polymerization method using melamine as the raw material, bismuth nitrate pentahydrate (Bi(NO3)3·5H2O) as the dopant source, and nitric acid (HNO3) and acetic acid (AC) as soft templates for the ultrathin nanosheets construction. The Bi-CNNS catalysts exhibited an excellent photocatalytic performance in tetracycline (TC) degradation. The TC removal efficiency reached to be 94.1% in 30 min under visible-light irradiation over 0.03Bi-CNNS, which is 6.03 times higher than that of pure g-C3N4 (CN). The higher specific surface area, narrower bandgap, the improved photoexcited electron-hole pair transfer and separation efficiency, and prolonged carrier lifetimes in the Bi3+-doped ultrathin g-C3N4 nanosheets led to a significantly enhanced photocatalytic performance. The main radical species responsible for the degradation of tetracycline over 0.03Bi-CNNS were O2- and OH. Moreover, the possible photodegradation intermediate products of TC were detected by gas chromatography-mass spectroscopy (GC-MS), and a possible pathway was proposed.

Use of anaerobic hydrolysis pretreatment to enhance ultrasonic disintegration of excess sludge.

To improve the excess sludge disintegration efficiency, reduce the sludge disintegration cost, and increase sludge biodegradability, a combined pretreatment of anaerobic hydrolysis (AH) and ultrasonic treatment (UT) was proposed for excess sludge. Results showed that AH had an advantage in dissolving flocs, modifying sludge characteristics, and reducing the difficulty of sludge disintegration, whereas UT was advantageous in damaging cell walls, releasing intracellular substances, and decomposing macromolecular material. The combined AH-UT process was an efficient method for excess sludge pretreatment. The optimized solution involved AH for 3 days, followed by UT for 10 min. After treatment, chemical oxygen demand, protein, and peptidoglycan concentrations reached 3,949.5 mg O2/L, 752.5 mg/L and 619.1 mg/L, respectively. This work has great significance for further engineering applications, namely, reducing energy consumption, increasing the sludge disintegration rate, and improving the biochemical properties of sludge.

Study on the spatial distribution of the liquid temperature near a cavitation bubble wall.

A simple new model of the spatial distribution of the liquid temperature near a cavitation bubble wall (Tli) is employed to numerically calculate Tli. The result shows that Tli is almost same with the ambient liquid temperature (T0) during the bubble oscillations except at strong collapse. At strong collapse, Tli can increase to about 1510 K, the same order of magnitude with that of the maximum temperature inside the bubble, which means that the chemical reactions occur not only in gas-phase inside the collapsing bubble but also in liquid-phase just outside the collapsing bubble. Four factors (ultrasonic vibration amplitude, ultrasonic frequency, the surface tension and the viscosity) are considered to study their effects for the thin liquid layer. The results show that for the thin layer, the thickness and the temperature increase as the ultrasonic vibration amplitude rise; conversely, the thickness and the temperature decrease with the increase of the ultrasonic frequency, the surface tension or the viscosity.