Stanene is a quantum spin Hall insulator and a promising material for optoelectronic and electronic devices. Density functional theoretical (DFT) calculations are performed to understand the effect of elemental doping (In, Sb, and In-Sb) towards gas sensor and photocatalytic applications. The In/Sb doping in stanene enhances the formation of Lewis acid-base adducts with N-based gas molecules, which in turn improves the sensitivity and selectivity towards a particular gas molecule. Moreover, such stanene based systems show excellent energetic, thermal, dynamical, and mechanical stability and band edge potential, which further suggests that they can be synthesized and used for various applications.