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This work aims to design two-dimensional (2D) catalysts based ZnO and ZnS for CO2 reduction reaction (CRR), nitrogen reduction reaction (NRR), CO2 and N2 captures and sensors. Cheap and abundant elements which are Mg, Cl, and N are doped into Zn, S, and O sites to tune the electronic properties of the ZnO and ZnS monolayers. Also, influences of O, S and Zn vacancies on the electronic properties and gas adsorption are examined as well. Adsorption energy, interaction energy, distortion energy, density of states, Bader charge, shift of Fermi level, and work function of the modified surfaces are studied via density functional theory (DFT) performed on VASP. From the results, Mg, Cl, and N doping as well as vacant sites can extremely change electronic properties, i.e., semiconductive to metallic behavior, the shift of Fermi level and the variation of work function. Some modified ZnS and ZnO monolayers can be good candidates CRR and NRR catalysts since neither too strong nor too light binding of CO2, CO and N2. The best catalysts for this study is (Mg, VZn)-ZnO and Cl-ZnS because both can be sensors and electrochemical catalysts due to the proper binding strength for CO2, CO and N2 adsorption. The change in the electronic properties leading to the change in gas adsorption shows that the ZnO and ZnS modification by cheap-element doping and vacancy-site creation are potential ways to improve their properties, extend their applications and lead to the invention promising catalysts for electrochemical reactions, gas sensors and gas storages.