Nitrogen-Doped Carbon Dots Induced Enhancement in CO2 Sensing Response From ZnO-Porous Silicon Hybrid Structure.

Jesús A Ramos-Ramón,Naveen K R Bogireddy,Vivechana Agarwal,Tangirala V K Karthik,Jorge Arturo Giles Vieyra

doi:10.3389/fchem.2020.00291

Abstract

In this study, we report a simple method for the fabrication of carbon dots sensitized zinc oxide–porous silicon (ZnO–pSi) hybrid structures for carbon dioxide (CO2) sensing. A micro-/nanostructured layer of ZnO is formed over electrochemically prepared pSi substrates using a simple chemical precipitation method. The hybrid structure was structurally and optically characterized using scanning electron microscopy, X-ray diffraction, fluorescence, and cathodoluminescence after the incorporation of hydrothermally prepared nitrogen-doped carbon dots (NCDs) by drop casting. With respect to the control sample, although all the devices show an enhancement in the sensing response in the presence of NCDs, the optimal concentration shows an increase of ~37% at an operating temperature of 200°C and a response time <30 s. The increment in the CO2-sensing response, upon the addition of NCDs, is attributed to an increase in CO2-oxygen species reactions on the ZnO surface due to an increment in the free electron density at the metal–semiconductor-type junction of NCD clusters and ZnO micro-/nanorods. A significant increase in the sensing response (~24%) at low operating temperature (100°C) opens the possibility of developing very large-scale integrable (VLSI), low operational cost gas sensors with easy fabrication methods and low-cost materials.

Highlights

Chemical sensors have been in high demand due to their application in various fields such as environmental pollution monitoring and control, healthcare, food industries, etc. (Choi et al, 2019)
zinc oxide–porous silicon (ZnO–pSi) and nitrogen-doped carbon dots (NCDs)–ZnO–pSi hybrid structures were fabricated for the detection of different concentrations of CO2 at two different operational temperatures utilizing simple easy chemical synthesis routes
Prepared NCDs were deposited onto the porous substrates covered with ZnO–pSi hybrid structures by drop-casting technique and characterized using field-emission scanning electron microscope (FESEM) and PL and CL spectroscopies

Summary

INTRODUCTION

Chemical sensors have been in high demand due to their application in various fields such as environmental pollution monitoring and control, healthcare, food industries, etc. (Choi et al, 2019). The fabricated sensor was able to detect H2S in low concentration (down to 2 ppm) due to the release of oxygen molecules during thermal reduction and evaporation of the by-product process Those oxygen molecules are adsorbed on the surface of ZnO nanorods (NRs) improving gas sensitivity. Gas-sensing mechanism is based on the adsorption of CO2 molecules on the metal oxide semiconductor surface in different sites (metal or oxygen sites) at different temperatures resulting in an increase in surface resistance depending upon the concentration of CO2 molecules. Mendoza-Agüero et al (2014) fabricated electrochemically grown WO3 films deposited over macroporous silicon substrates They studied the effect of annealing temperature in the electrical properties of the hybrid structures and utilized them for ethanol vapors sensing at a concentration up to 1 ppm. ∼24 and ∼37% under a CO2 concentration of 15 ppm for operating temperatures of 100 and 200◦C, respectively, opening the possibility for developing low-cost VLSI compatible solidstate sensors

EXPERIMENTAL PROCEDURE

RESULTS AND DISCUSSION

CONCLUSIONS

DATA AVAILABILITY STATEMENT