P-n Transition-Enhanced Sensing Properties of rGO-SnO2 Heterojunction to NO2 at Room Temperature

Abstract

RGO-SnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> heterojunction has been extensively studied as an efficient sensitive material, while its sensing mechanism in surface chemical system is still needed to be concerned. The aim of this work is to evaluate the effects of rGO and materials processing on surface sites of nanocrystalline tin dioxide and room-temperature sensitivity to NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> . Gas-sensitive heterojunction of tin dioxide with 2-dimensional rGO has been synthesized by a one-step hydrothermal method. Contrastive researches about composition, microstructure and surface species of hydrothermalobtained pristine SnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , rGO-SnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> hybrids were performed. Further reduction of rGO in hydrothermal composite with a post-treatment at over 100 °C has been found to affect the hydrophilicity and electrical conduction of rGO-SnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> composite. Sensitivity of rGO-SnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> to 2-8 ppm NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> with fast response was demonstrated at room temperature, while the abrupt change of conductivity type of hydrothermal-obtained rGO-SnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> heterojunction from p-type to n-type was observed after post-anneal treatment. The conductive type conversion was discussed to be closely related to the higher reduction degree of rGO and enhanced hydrophobic surface of rGO-SnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> heterojunction.