Pulsed laser deposition was employed to accurately vary the BiVO4 content on the outermost surface of black TiO2 (B-TiO2) nanotube arrays. The optimal B-TiO2(225) led to >80% tetracycline (TC) antibiotic removal, while only 27% TC removal was obtained by bare TiO2 nanotubes after 300 min of photocatalytic reaction under visible-light irradiation. Moreover, the removal rate constant using the optimal heterojunction sample was 0.005 min–1, which was more than 5 times higher than that of bare TiO2 nanotubes. Such an improvement in the performance was attributed to the one-dimensional structure, enhanced light absorption of B-TiO2, formation of a thermodynamically favorable type II heterojunction, and deposition of BiVO4 on the top surface of B-TiO2, which increases the light utilization in front illumination. On the basis of the identification of intermediates and byproducts via high-resolution tandem mass spectrometry analysis and the Fukui index, it was revealed that demethylation and oxidation were the main degradation pathways. The toxicity change after treatment was assessed by using the optical density method and the Ecological Structure Activity Relationship (ECOSAR) program. The results indicate that the mass ratio between B-TiO2 and BiVO4 is a critical parameter for determining the photocatalytic activity, in terms of not only the TC degradation efficiency and kinetics but also the type and quantity of byproducts and, hence, the toxicity of the treated solution.

Biomass-waste activated carbon/molybdenum oxide/molybdenum carbide ternary composites are prepared using a facile in-situ pyrolysis process in argon ambient with varying mass ratios of ammonium molybdate tetrahydrate to porous peanut shell activated carbon (PAC). The formation of MoO2 and Mo2C nanostructures embedded in the porous carbon framework is confirmed by extensive structural characterization and elemental mapping analysis. The best composite when used as electrodes in a symmetric supercapacitor (PAC/MoO2/Mo2C-1//PAC/MoO2/Mo2C-1) exhibited a good cell capacitance of 115 F g−1 with an associated high specific energy of 51.8 W h kg−1, as well as a specific power of 0.9 kW kg−1 at a cell voltage of 1.8 V at 1 A g−1. Increasing the specific current to 20 A g−1 still showcased a device capable of delivering up to 30 W h kg−1 specific energy and 18 kW kg−1 of specific power. Additionally, with a great cycling stability, a 99.8% coulombic efficiency and capacitance retention of ~83% were recorded for over 25,000 galvanostatic charge-discharge cycles at 10 A g−1. The voltage holding test after a 160 h floating time resulted in increase of the specific capacitance from 74.7 to 90 F g−1 at 10 A g−1 for this storage device. The remarkable electrochemical performance is based on the synergistic effect of metal oxide/metal carbide (MoO2/Mo2C) with the interconnected porous carbon. The PAC/MoO2/Mo2C ternary composites highlight promising Mo-based electrode materials suitable for high-performance energy storage. Explicitly, this work also demonstrates a simple and sustainable approach to enhance the electrochemical performance of porous carbon materials.

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