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

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 (CO 2 ) 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 CO 2 -sensing response, upon the addition of NCDs, is attributed to an increase in CO 2 -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.

Carbon dot/inorganic nanomaterial composites

“…7c). Similarly, studies in recent years show that ZnO-based energy storage devices are the development trend in the future energy eld, [102][103][104] but the development of high performance nickel-zinc (Ni-Zn) alkaline batteries is troubled by the short life and poor rate performance of ZnO anode materials. 27 Interestingly, researchers found that CDs controlled the growth of ZnO.…”

Recent development in carbon dot-based gas sensors

“…Silica aerogel-PEI capped CQDs exhibits 30nm blue shift in FL wavelength as compared to CQDs in aqueous solution due to strong electrostatic interaction between the negatively charged silica surfaces and the positively charged PEI on the surface of the CQDs [86]. In CD grafted ZnO-pSi, electrons transits to LUMO of N-CD on excitation and emits green luminescence on relaxation as opposed to blue FL by bare N-CDs as shown in figure 7c [70]. Among -N, R-NH and -NH 2 groups, -N has the highest positive impact while among the -SH, -SR and =S groups, -SH has the highest positive impact on the optical performance of CDs.…”

“…It is a widely adopted CD synthesis method as it is eco-friendly, but requires high reaction temperature and time [13,16]. A wide variety of precursors such as citric acid [36,49,52,68,69,71], urea [4,68,70], polyamines [37] and biological precursors such as carbohydrates [13,72], amino acids, lignin, mushroom [4] and polymers [73] etc, were employed for CD synthesis through hydrothermal/ microwave-assisted methods [4]. Furthermore, soft template or hard template method where graphite like planar and highly symmetric molecules such as 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) or hexa-peri-hexabenzo-coronene (HBC) was used as carbon precursor and template [2,12,13].…”

“…Figure 23 -(A) Schematic of the mechanism of (a) ZnO and (b) ZnO:GQDs under relative humidity (c) ZnO:GQDs and (d) Magnified view of ZnO:GQDs on exposure to NH 3 under relative humidity; (B) Response curve of ZnO-GQDs sensor towards different concentrations of NH 3 [67]; (C) Schematic diagram of O 2 and CO 2 adsorption on sensors of (a),(b) ZnO and (c),(d) ZnO-NCDs respectively[70] …”

Carbon Dots: Classification, Properties, Synthesis, Characterization, and Applications in Health Care—An Updated Review (2018–2021)

“…Recently, several gas sensors involving the use of CDs were reported. For instance, El-Shamy designed a CDs-functionalized magnesium oxide (MgO) nano-particle (CDs@MgO) sensor for sensing hydrogen sulfide (H 2 S) gas [282], Ramos-Ramón et al developed a N-CDs based sensor for CO 2 [283], Wang et al fabricated silica aerosol-modified CDs-based gas sensor for NO 2 monitoring [284], and Carbone prepared a CDs-assembled nickel oxide (NiO)-based sensor for methane gas detection [285]. However, most of the CDs-based gas sensors reported to date were developed for environmental monitoring and safety, it is speculated that CDs-based gas sensors will be a promising research area in the near future for serving biomedical applications as well.…”