This paper develops a novel ultrasonic spray-assisted solvothermal (USS) method to synthesize wrapped ZnO/reduced graphene oxide (rGO) nanocomposites with a Schottky junction for gas-sensing applications. The as-obtained ZnO/rGO- x samples with different graphene oxide (GO) contents ( x = 0–1.5 wt %) are characterized by various techniques, and their gas-sensing properties for NO 2 and other VOC gases are also evaluated. The results show that the USS-derived ZnO/rGO samples exhibit high NO 2 -sensing property at low operating temperatures (e.g., 70–130 °C) because of their high specific surface area and porous structures when compared with the ZnO/rGO sample obtained by the traditional precipitation method. The content of rGO shows an obvious effect on their NO 2 -sensing properties, and the ZnO/rGO-0.5 sample has a high response of 62 operating at 130 °C, three times that of pure ZnO. The detection limit of the ZnO/rGO-0.5 sensor to NO 2 is as low as 10 ppb under the present test condition. In addition, the ZnO/rGO-0.5 sensor shows a highly selective response to NO 2 gas when compared with organic vapors and other inflammable or toxic gases. The theoretical and experimental analyses indicate that the enhancement in NO 2 -sensing performance of the ZnO/rGO sensor is attributed to the formation of wrapped ZnO/rGO Schottky junctions.

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Nowadays, ozone (O 3 ) has become a worldwide pollutant, and it is challenging to prepare monolithic O 3 decomposition catalysts substituting the conventional complicated process of adhering catalyst powders onto porous substrates. Herein, monolithic Cu 2 O−CuO/Cu catalysts are obtained facilely by in situ thermal oxidizing− reducing copper foam. After optimization, the CuO nanowires (NWs) are first produced by annealing Cu foam in O 2 at 400 °C for 2 h and then the NW surface is reduced into Cu 2 O by annealing in Ar/H 2 at 350 °C for 2 h. The obtained Cu 2 O−CuO/Cu monolithic catalyst exhibits high catalytic activity to 20 ppm O 3 , maintaining 100% at a space velocity of 11,000 h −1 and even about 94% at 38,000 h −1 . The catalytic ability toward O 3 can be attributed to the generated Cu + /Cu 2+ redox couples, the donor/acceptor-type point defects, and the Cu 2 O−CuO p−p heterojunction. This demonstrates the successful and convenient preparation of the monolithic catalyst for rapid, controllable, and productive O 3 removal applications.

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In recent years, researchers have spent much effort on the development of specific catalytic materials for ozone decomposition, yet investigation on its mechanism is still needed. In this work, a semiconductor metal oxide catalyst strengthened by the Mott−Schottky effect is prepared. In several synthesized Cu/ Cu 2 O samples, the scale of heterojunctions is adjusted during synthesis, and its influence is investigated by varieties of characterization techniques. In the catalytic test of ozone decomposition, ozone conversion reached 92% at a high weight hourly space velocity (WHSV) of 1,920,000 cm 3 g −1 h −1 , and compared with the control group without a heterojunction, it has obvious performance improvement. In this work, the application feasibility of the Mott− Schottky effect in the ozone decomposition field is researched from the version of the carrier transfer mechanism. This work proves that the Cu/Cu 2 O heterojunctioned catalyst has great application prospects; meanwhile, it also provides a new idea for finding other suitable catalysts for ozone decomposition.

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