The results of carbon-doped zinc oxide nanoparticles synthesized by CO2 microwave plasma at atmospheric pressure are presented. The 2.45-GHz microwave plasma torch and feeder for injecting Zn granules are used in the synthesis of zinc oxide nanoparticles. The Zn granules (13.5？g/min) were introduced into the microwave plasma by CO2 (5？l/min) swirl gas. The microwave power delivered to the CO2 microwave plasma was 1？kW. The synthesis of carbon-doped zinc oxide nanoparticles was carried out in accordance with CO2？+？Zn？→？carbon-doped ZnO？+？CO. The synthesized carbon-doped zinc oxide nanoparticles have a high purity hexagonal phase. The absorption edge of carbon-doped zinc oxide nanoparticles exhibited a red shift from a high-energy wavelength to lower in the UV-visible spectrum, due to band gap narrowing. A UV-NIR spectrometer, X-ray diffraction, emission scanning electron-microscopy, energy dispersive X-ray microanalysis, Fourier transform infrared spectroscopy, and a UV-Vis-NIR spectrophotometer were used for the characterization of the as-produced products. 1. Introduction CO2 has been verified as a significant factor in the increase of the greenhouse effect. The decomposition and extinction of CO2 are very important to environmental factors. Recently, CO2 capture and storage (CCS) [1, 2], CO2 capture and utilization (CCU) [3], and CO2 reforming of CH4 [4] are being used as technology for recycling CO2. CCU is among the more promising of these technologies being deployed. In order to utilize the oxygen in CO2 as an oxidant, the synthesis method of carbon-doped zinc oxide nanoparticles (C-doped ZnO-NPs) using a CO2 microwave plasma torch has been designed. The developed CO2 microwave plasma torch operated at atmospheric pressure seems to have demonstrated high potential for the synthesis of C-doped ZnO. The UV near-band edge emission of pure ZnO catalyst is detected in approximately 380？nm (~3.2？eV). Therefore, a band gap of Pure ZnO does not allow the capture of most of the solar light energy [5]. Only a small portion (UV energy) of the solar spectrum is absorbed. Consequently, a major issue of ZnO catalyst production is the need to increase the efficiency of photo-activity by band gap narrowing. The band gap narrowing of photo-catalyst is obtained by the inclusion of transition metals (V, Cr, Mn, and Fe) or main group atoms (N, C, S, and F). As a typical example, impurities such as transition metals, nitrogen, sulphur, and carbon can be doped in oxygen vacancy or the lattice of a ZnO catalyst using one of several synthesis ways. Various transition
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