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Pristine and Doped MoS2 Monolayers as Potential HCN Gas Sensors: A DFT Study

Neeraj Thakur, Anjna Bhardwaj, Arun Kumar, Amarjeet Singh

TL;DR

The paper uses density functional theory to evaluate pristine and doped $MoS_2$ monolayers as HCN gas sensors, exploring adsorption energetics, recovery times, and changes in electronic and optical properties. It finds that Al-doping induces chemisorption with the strongest binding, while most dopants yield physisorption; adsorption strength and recovery can be tuned by introducing multiple dopants, sometimes strengthening and other times weakening adsorption. Among doped systems, $2X$ configurations (e.g., 2P–MoS$_2$) provide favorable adsorption with nanosecond to microsecond recovery, whereas certain $3X$ configurations (notably 3Al–MoS$_2$) offer distinct trade-offs between signal strength and desorption time, including a recovery time of about $1.74$ s. The results also show substantial band-gap, work-function, and UV optical changes, highlighting potential for both chemiresistive sensing and UV-range optical sensing in doped MoS$_2$ platforms. Overall, the study identifies promising doped MoS$_2$ candidates for fast, reusable HCN sensing and suggests avenues for tuning sensor performance via dopant concentration and composition.

Abstract

Two-dimensional transition metal dichalcogenides (TMDCs) have been extensively investigated due to their tunable properties. In this work, density functional theory (DFT) is employed to investigate the adsorption behavior and sensing characteristics of HCN on pristine and doped MoS2 monolayers (X-MoS2, where X = P, N, Si, Al, B, Cl). The structural, electronic, and optical characteristics of all systems are examined to study the sensing properties of various doped MoS2 monolayers. In particular, the Al-MoS2 system demonstrates the strongest adsorption characterized by chemisorption, while the remaining systems show interactions of physisorption type. Recovery time and changes in electronic and optical properties reveal that Si-MoS2 possesses an ultrafast response of the order of microseconds, while Al-MoS2 exhibits a significantly longer recovery time, making it unsuitable for reusable sensors. P-MoS2, Si-MoS2, and Al-MoS2 monolayers show pronounced changes in their properties after HCN adsorption. To explore tunability in adsorption strength and recovery behavior, systems with two and three dopant atoms are further studied for P, Si, and Al doping. The results indicate that double doping enhances adsorption strength, whereas triple symmetric doping weakens it. Based on adsorption energy, recovery time, and electronic response, 2P-MoS2 and 3Al-MoS2 are identified as promising candidates for electrochemical and chemiresistive sensing of HCN. Additionally, the observed optical response in the ultraviolet region highlights their potential in UV-range optical sensor design.

Pristine and Doped MoS2 Monolayers as Potential HCN Gas Sensors: A DFT Study

TL;DR

The paper uses density functional theory to evaluate pristine and doped monolayers as HCN gas sensors, exploring adsorption energetics, recovery times, and changes in electronic and optical properties. It finds that Al-doping induces chemisorption with the strongest binding, while most dopants yield physisorption; adsorption strength and recovery can be tuned by introducing multiple dopants, sometimes strengthening and other times weakening adsorption. Among doped systems, configurations (e.g., 2P–MoS) provide favorable adsorption with nanosecond to microsecond recovery, whereas certain configurations (notably 3Al–MoS) offer distinct trade-offs between signal strength and desorption time, including a recovery time of about s. The results also show substantial band-gap, work-function, and UV optical changes, highlighting potential for both chemiresistive sensing and UV-range optical sensing in doped MoS platforms. Overall, the study identifies promising doped MoS candidates for fast, reusable HCN sensing and suggests avenues for tuning sensor performance via dopant concentration and composition.

Abstract

Two-dimensional transition metal dichalcogenides (TMDCs) have been extensively investigated due to their tunable properties. In this work, density functional theory (DFT) is employed to investigate the adsorption behavior and sensing characteristics of HCN on pristine and doped MoS2 monolayers (X-MoS2, where X = P, N, Si, Al, B, Cl). The structural, electronic, and optical characteristics of all systems are examined to study the sensing properties of various doped MoS2 monolayers. In particular, the Al-MoS2 system demonstrates the strongest adsorption characterized by chemisorption, while the remaining systems show interactions of physisorption type. Recovery time and changes in electronic and optical properties reveal that Si-MoS2 possesses an ultrafast response of the order of microseconds, while Al-MoS2 exhibits a significantly longer recovery time, making it unsuitable for reusable sensors. P-MoS2, Si-MoS2, and Al-MoS2 monolayers show pronounced changes in their properties after HCN adsorption. To explore tunability in adsorption strength and recovery behavior, systems with two and three dopant atoms are further studied for P, Si, and Al doping. The results indicate that double doping enhances adsorption strength, whereas triple symmetric doping weakens it. Based on adsorption energy, recovery time, and electronic response, 2P-MoS2 and 3Al-MoS2 are identified as promising candidates for electrochemical and chemiresistive sensing of HCN. Additionally, the observed optical response in the ultraviolet region highlights their potential in UV-range optical sensor design.
Paper Structure (9 sections, 9 equations, 14 figures, 6 tables)

This paper contains 9 sections, 9 equations, 14 figures, 6 tables.

Table of Contents

  1. Introduction
  2. Computational Methodology
  3. Results and Discussion
  4. Optimised geometries of pristine and doped MoS2 monolayers
  5. Adsorption of HCN on pristine and doped monolayers
  6. Electronic Properties
  7. Optical properties
  8. Recovery Time Modulation through Doping
  9. Conclusion

Figures (14)

  • Figure 1: Optimized structure of the $6 \times 6 \times 1$ 1H-MoS$_2$ supercell (left) and HCN molecule (right). The circled sulfur atom is substituted with an X atom (X = P, N, Si, Al, B, Cl).
  • Figure 2: Optimised structure of $HCN$-molecule adsorbed on doped-monolayers of type (a) Cl-MoS$_2$, (b) N-MoS$_2$, (c) Pristine MoS$_2$, (d) P-MoS$_2$, (e) B-MoS$_2$, (f) Si-MoS$_2$, (g) Al-MoS$_2$ monolayer. The circled atom indicates the dopant atom in pristine monolayer.
  • Figure 3: Adsorption energy ($E_{\text{ads}}$) trends for pristine and X-doped MoS$_2$ monolayers
  • Figure 4: Electronic band structures of (a) Pristine MoS$_2$, (b) P–MoS$_2$, (c) N–MoS$_2$, (d) Si–MoS$_2$, (e) Al–MoS$_2$, (f) B–MoS$_2$, and (g) Cl–MoS$_2$ monolayers before HCN adsorption (top) and after HCN adsorption (bottom). In all cases, the Fermi level is set to 0 eV and is represented by horizontal dotted green line. Vertical dotted red lines indicate the high-symmetry points in the Brillouin zone.
  • Figure 5: Total density of states (TDOS) of (a) Pristine MoS$_2$, (b) P–MoS$_2$, (c) N–MoS$_2$, (d) Si–MoS$_2$, (e) Al–MoS$_2$, (f) B–MoS$_2$, and (g) Cl–MoS$_2$ monolayers before and after HCN adsorption. In all cases, the Fermi level is set to 0 eV and is represented by a vertical dotted green line.
  • ...and 9 more figures