A comprehensive review on functionalized Hydroxyapatite nanostructures based gas sensors for environmental pollutant monitoring

Abstract

The utilization of advanced sensing techniques for detecting and monitoring toxic gases in industry and the environment is a predominant action. For such applications, the sensor material should possess higher sensitivity, faster detection, and real-time operation. Mostly, metal oxides (MOs) are preferred for gas sensing purposes owing to their excellent sensing property, wide band-gap, electrical conductivity, and high surface reactivity. But, the same MOs lag in many perspectives like low selectivity, higher operating temperature (> 400 °C), more power consumption, and reduced stability. Since more emphasis is given to materials that operate at room temperatures like nano-hydroxyapatite (nHAp), it’s a bio-ceramic material used for chemical gas sensing. The nHAp is a matrix of rich calcium (Ca²⁺) and phosphate (PO₄^3-) ions. In chemical gas sensors, the nHAp possess significant properties like large surface phosphate-hydroxide (P-OH) groups, ionic conductivity, porous nature, and ion exchange capability for effective gas molecule interaction. In this profound review, we discussed the nHAp structure with different fabrication techniques for gas sensing. Particularly, functionalized nHAp with MO and polymers were focused and their stability, sensitivity, selectivity, and adsorption rate are presented along with different mechanisms. Existing challenges and future perspectives of nHAp material are also highlighted.