Liquid-phase Exfoliation Process Research Articles

Photovoltaic induced self-powered gas sensor based on 2D MoS2 incorporated NbSe2 nanorods heterostructure for NH3 gas sensing at room temperature

Two-dimensional (2D) transition metal dichalcogenides (TMDs) have attracted significant attention for their optical and gas-sensing applications due to their exceptional sensitivity. Reliable selectivity and low power consumption are two major requirements for photodetector and gas sensor applications in next-generation electronic devices and the Internet of Things. Self-powered sensors (especially photovoltaic gas sensors) can solve these problems. In this study, for the first time, we report 2D TMDs (NbSe2-MoS2 hybrid) on a SiO2/Si substrate to fabricate photovoltaic self-powered gas sensors. The gas sensors are operated by the photovoltaic effect of the NbSe2-MoS2 nanostructure, which is prepared using the liquid phase exfoliation process. Initially, it was revealed that the present hybrid material exhibits photovoltaic properties under light illumination, with a circuit current of 0.25 µA and a circuit voltage of 34 mV. The NbSe2-MoS2 nanostructure characteristics were then used for NH3 gas sensing at different concentrations, and the gas sensing response was detected from low (8.8 % at 10 ppm) to high (28.8 % at 500 ppm) concentrations. The built-in electric field occurred between the NbSe2-MoS2 junction and eventually operated as a driving force for NbSe2-MoS2 gas sensing without an external bias voltage. The physisorption of gas molecules on their surface prompts a charge-transfer mechanism that improves the gas sensor response. The combined outcome of NbSe2-MoS2 heterostructures could pave way to next-generation gas sensing device fabrications.

Sub-nanosecond single mode-locking pulse generation in an intracavity KTP optical parametric oscillator with a few-layer Bi2Te3 topological insulator saturable absorber

By utilizing the ultrasound-assisted liquid phase exfoliation process, Bi2Te3 nanosheets are synthesized and deposited onto a quartz plate to form a saturable absorber (SA), in which nonlinear absorption characteristics around 1 μm are investigated with a home-made Q-switched laser. With the as-prepared Bi2Te3 SA employed, a sub-nanosecond KTiOPO4 (KTP) based intracavity optical parametric oscillator (IOPO) pumped by a dual-loss-modulated Q-switched and mode-locked (QML) laser is successfully realized. With a short duration of sub-nanosecond and a repetition rate of several kilohertz (kHz), the signal wave’s single mode-locking pulse existed underneath a Q-switched envelope can be formed. At an incident pump power of 8.92 W and an acousto-optic modulator (AOM) repetition rate of 2 kHz, a signal wave’s single mode-locking pulse underneath a Q-switching envelope with a measured minimum pulse duration of 520 ps is accomplished. It is the first demonstration of such Bi2Te3 SA utilized in a solid-state QML IOPO laser, to the best of our knowledge. According to the experimental results, this provides an efficient and straightforward approach to acquire sub-nanosecond OPO signal wave pulses. Additionally, the relevant coupled rate equations are established, and the simulation results match the experimental results, revealing the potential of Bi2Te3 as a nanomaterial for optoelectronic applications.

Solution blending preparation of polyurethane/graphene composite: Improving the mechanical and anti-corrosive properties of the coating on aluminum surface

Graphene-based polyurethane composites (PU/G) are prepared by a simple solution blending method to disperse defect-free graphene flakes (prepared via liquid phase exfoliation process) into the polyurethane matrix. The PU/G composite with 1 wt% of graphene flakes performs the significant improvement (∼50 %) of the impact strength (124 kg.cm) and adhesion behavior (∼2.3 MPa) with respect to that of pristine PU. The PU/G coating with 2 wt% of graphene achieves the highest long-term anti-corrosion performance after 150 immersed days in 3 wt% NaCl solution (with the stable impedance modulus of ∼2.7 × 1010 Ω.cm2) or after 2500 h of salt spray exposure in 5 wt% NaCl solution (no corrosive traces detected on aluminum substrate).

Improving the liquid phase exfoliation efficiency of graphene based on the enhanced intermolecular and interfacial interactions

The liquid phase exfoliation (LPE) technique presents significant advantages and potential for the large-scale production of high-quality graphene nanosheets (GNs) with minimal defects. Nevertheless, the Hansen solubility parameters and surface tension matched principle were limited the range of suitable solvents for LPE process. As a result, commonly employed solvents such as N-methyl-2-pyrrolidone (NMP) and N, N-Dimethylformamide (DMF) exhibit low viscosity, leading to a low transmission efficiency of shear force from solvent to graphite, resulting in inadequate shear force and low exfoliation efficiency. In this work, to break through limitations of existing solvent systems, we investigate the influence of solvent viscosity on the LPE efficiency in various pyrrolidone solvents, which share similar structures with NMP but have longer molecular chains and higher viscosity. When compared to the NMP system, the concentration of GNs in the N-octyl-2-pyrrolidone (NOP) suspension system exhibits a significant increase of approximately 70 %, which primarily attributed to the higher intermolecular and interfacial interactions in NOP suspension. Moreinterestingly, the interactions could be further intensified by reducing the operating temperature in the NOP suspension system, which leading to an about 150 % improvement in LPE efficiency when compared to the NMP system at standard temperature. Given the remarkable conductivity of GNs, the prepared Cellulose nanofibers/graphene nanosheets (CNF/GNs) composite film exhibits lightweight and efficient electromagnetic shielding performance of 2.4 × 104 dB cm2 g−1.This work is expected to establish a universal and efficient pathway for the economical and high-yield production of GNs, elucidating the microscopic mechanism by which molecular conformation at the solid–liquid interface influences the transfer of shear forces from solvent to graphite, thereby promoting the development of widespread applications of GNs ang other two-dimensional (2D) nanomaterials.

Study of the Hydrogen Evolution Reaction on Macroscopic Snse-Based Photoelectrodes

Conversion of solar energy to valuable chemicals by using photoelectrochemical (PEC) techniques such as water splitting, carbon dioxide reduction reaction (CO2RR) and nitrogen reduction reaction (N2RR), are promising methods to solve the issues of energy crisis and global warming [1-2]. Two-dimensional (2D) and layered semiconductors, for example, transition metal chalcogenides (TMCs), metal oxides and MXenes have attracted great attention for PEC applications because of their unique properties, such as high carrier mobility, tunable bandgap, anisotropic carrier transport, and high specific surface area [3]. Our review indicates that, i) 2D and layered semiconductors can be applied for different PEC applications, both in oxidation and reduction reactions, and have ability to give higher performance in water reduction (i.e., hydrogen evolution reaction, HER) than in the other ones. ii) TMCs have been the most studied material with higher performance than the others. However, high PEC performance was achieved only on single crystal TMCs or in microelectrochemical cells, implying a limitation in the scalability of this solar energy conversion approach [4]. There is a clear need to study macroelectrodes prepared from polycrystalline semiconductors and identify the opportunities and barriers for their applications. In our study [5], tin(II) selenide (SnSe) was used as a photoelectrode for PEC HER since it has not been widely investigated for this PEC application. We fabricated SnSe macroscopic photocathodes by depositing SnSe flakes, made from commercial SnSe crystals using a liquid phase exfoliation (LPE) method, on glassy carbon. The as-received SnSe crystals were exfoliated in isopropanol/water mixtures (IPA/H2O) and pure IPA, respectively. Pure IPA was found to be the optimal solvent to prepare flakes and for achieving the highest PEC activity. An additional size separation to make three different size fractions of SnSe crystals served to further optimize the LPE process. Electrodes prepared from the largest flakes showed the highest photocurrent density of 2.44 ± 0.65 mA cm–2 at –0.74 V vs. RHE. The photodeposited Pt co-catalyst on SnSe surface further accelerated the PEC HER activity to 4.39 ± 0.15 mA cm–2. Intensity modulated photocurrent spectroscopy results manifested that the Pt co-catalyst enhanced the charge transfer process and suppressed charge carrier recombination. Overall, the solvent for exfoliation, the edge density of SnSe nanoflakes, immobilization method, and Pt co-catalyst affected the PEC HER performance of SnSe. These results indicate the merit of employing SnSe electrodes for PEC HER and inspire us to explore other photoelectrocatalytic reactions on the macroscopic exfoliated SnSe electrodes.

Liquid Phase Graphene Exfoliation with a Vibration-Based Acoustofluidic Effector.

Liquid phase exfoliation (LPE) has emerged as a promising method for the industrial-scale production of graphene. However, one of its critical steps, namely sonication, has faced challenges due to high power consumption and low efficiency, leading to limited applicability in industrial settings. This study introduces a novel, cost-effective microfluidic sonication device designed to significantly reduce power consumption while efficiently assisting the LPE process for graphene production. By coupling a capillary with a buzzer and applying an appropriate electric signal, simulation and particle tracing experiments reveal the generation of robust shear forces resulting from acoustic streaming and cavitation when the capillary end is immersed in the liquid. For the first time, the capillary-based sonication device was effectively utilized for graphene exfoliation in a DMF (N,N-Dimethylformamide) + NaOH liquid phase system. The SEM (Scanning Electron Microscope) and Raman characterization results corroborate the successful exfoliation of 100 nm with thicknesses below 10 nm graphene sheets from graphite flakes using this pioneering device. The values of I2D/IG increase after processing, which suggests the exfoliation of graphite flakes into thinner graphene sheets. The vibration-based acoustofluidic effector represents a versatile and scalable miniature device, capable of being employed individually for small-batch production, thereby optimizing the utilization of raw 2D materials, particularly in experimental scenarios. Alternatively, it holds the potential for large-scale manufacturing through extensive parallelization, offering distinct advantages in terms of cost-efficiency and minimal power consumption.

Lignin-ultrasound method: Enhancement of antimicrobial capacity of MoS2-containing films

To improve the antimicrobial ability of MoS2-containing films, we used lignin and triple-frequency ultrasound for liquid-phase exfoliation (LPE) to obtain MoS2 nanosheets. Photoresponsive antimicrobial films with MoS2 nanosheets, lignin, polyvinyl alcohol and deep eutectic solvents were subsequently prepared. Lignin functionalized the MoS2 nanosheets by chemically linking with S in MoS2 and significantly improved the exfoliation efficiency. Tri-frequency ultrasound produces beneficial effects on the LPE process by creating a more homogeneous sound field and a stronger degree of cavitation. The concentration of MoS2 nanosheets in the exfoliating solution could reach 1.713 mg/mL under the effect of lignin-ultrasound. The antimicrobial ability of the films was analyzed, and the colony-forming units of E. coli and S. aureus could be reduced from 7 × 106 to 1 × 106 cfu/mL under the irradiation of infrared. The lignin in the film undergoes depolymerization and demethoxylation under the irradiation of infrared to have a more phenolic hydroxyl structure, which confers the growth inhibition ability of the films for bacteria that cannot be in close contact with the film. The method we used has some significance for the preparation of MoS2 nanosheets, and composite films prepared from MoS2, and lignin can be used in food packaging, wound antimicrobials, and other fields.

Entropy-driven liquid-phase exfoliation of non-Van-Der-Waals crystals into nanoplatelets

Liquid-phase exfoliation (LPE) methods have revolutionized the production of two-dimensional (2D) materials from layered crystals, employing techniques such as ultrasonic degradation, mechanical exfoliation, and electrochemical exfoliation. However, the exfoliation of three-dimensional (3D) crystals that are nonlayered and non-Van-Der-Waals presents both challenges and opportunities. This study introduces an atomistic biaxial shear-normal strain entropy analysis to comprehend and design the LPE process specifically for such materials. By analysing the atomistic compressive biaxial shear-normal strain induced during LPE in 3D crystals, we establish a strain–stress-entropy relationship and derive a general exfoliation rate equation. We validate our model by comparing it to literature-based alloy exfoliation tests and conducting new Mg(OH)2 LPE (ball milling) experiments. The results not only confirm the applicability of the derived equation but also provide valuable insights into the exfoliation process. The implications of these findings are substantial, as they open new possibilities in various applications by informing the selection of 3D crystals and facilitating the design and optimization of LPE processes.

Energy harvesting using two-dimensional magnesiochromite (MgCr2O4)

Two-dimensional (2D) materials with high surface activity can be utilized for harvesting energy from small mechanical sources using flexoelectricity. In the present work, we have synthesized an atomically thin 2D spinel MgCr2O4 by a liquid-phase exfoliation process, and characterization shows the preferential exfoliation along the (111) plane with low formation energy. The fabricated flexoelectric device produces an electrical response up to ∼3 V (peak-to-peak voltage) upon pressing and releasing the cell with ∼0.98 N force. Furthermore, the energy harvesting properties of 2D MgCr2O4 are explored by combining bending with other sources of external energy, with applied varying magnetic flux (Vmax = ∼2.6 V) and temperature with 0.9 N force (Vmax = ∼18 V). Our calculations determine that 2D MgCr2O4 has a flexoelectric coefficient of approximately μXZXZ = 0.005 nC/m. Overall, the results indicate that 2D MgCr2O4 is a very promising material for the next generation of self-powered wearable electronics and energy harvesting.

Structure and physicochemical properties of MgB2 nanosheets obtained via sonochemical liquid phase exfoliation

We have performed ultrasonic liquid phase exfoliation (LPE) of MgB2 in ethanol and investigated the resulting nano-assemblies as a function of the ultrasound processing time. TEM morphological and structural analysis, along with STM topographic characterization, showed that for short sonication times the exfoliated grains preserve the MgB2 crystal structure, have a 2D character and produce Moiré patterns corresponding to stacked layers with rotational misalignment. On the other hand, the longest process times result in spheroidal nanoparticles with diameters of the order of 10 nm, which can also coalesce into larger agglomerates. Optical absorbance spectra confirmed that the exfoliated material preserves a metallic nature with a predominant 2D character corresponding to the ab-plane, whereas Raman spectra showed the presence of extra-modes induced by 3D symmetry breaking in the exfoliated products, along with indications of some B-H stretching modes. The detection of a positive zeta potential confirms that an active surface hydrogenation process has taken place during sonication. The mechanochemistry of the exfoliation mechanism has been attributed to particle–particle collisions and particle-shockwave interactions originating from the implosive bubble-collapse. The present study provides important information useful for implementing the LPE process in different contexts for MgB2, like few-layer superconductivity, antibacterial coating and nano-drug preparation.

A green approach to mica nanosheet production: Liquid-phase exfoliation in natural seawater

The development of environmentally friendly and sustainable methods for the exfoliation of nanosheets is of paramount importance in the field of nanotechnology. In this study, high-quality mica nanosheets (MNs) were prepared through a seawater-based liquid-phase exfoliation process that utilized ions intercalation for the first time. The morphological characteristics of the MNs were extensively characterized using various analytical techniques, such as field emission scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. Further analysis using X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and Raman spectroscopy confirmed the structural integrity and stability of the obtained MNs. Additionally, this work investigated the impact of reaction time, temperature, cycle number, and initial concentration on the production rate of MNs. Overall, this study highlights the potential of natural seawater as an effective solvent for the efficient exfoliation of high-quality MNs.

Development of a Smart and Ultrafast Flexible Humidity Sensor Using the 0D/2D Au/GeS Heterostructure for Human Respiration Rate Monitoring

We have developed a smart, Internet of Things (IoT)-enabled, intelligent, and flexible humidity sensor for human respiration rate monitoring by using a heterostructure of two-dimensional (2D) germanium(II) sulfide (GeS) and zero-dimensional (0D) gold nanoparticles (Au NPs). The 2D GeS was synthesized by a facile liquid-phase exfoliation process, followed by the post-functionalization of Au NPs. Furthermore, the chemical and structural integrities of the heterostructure were corroborated by microscopic and spectroscopic techniques. The as-prepared heterostructure (termed Au-GeS) exhibited a maximum sensor response of 7102% at 90% of relative humidity (RH) level compared to the pristine GeS sensor response of 2700% at the same RH level. Finally, we demonstrate the use of the Au-GeS flexible humidity sensor for human respiration rate monitoring. The sensor showed an ultrafast response and recovery times of 0.69 and 0.73 s, respectively, during exhalation and inhalation. The sensor was further integrated into a portable electronic system to facilitate IoT-enabled real-time wireless sensing at the smartphone application interface. In our study, the excellent sensor performance with a simple fabrication process offers utilization of the flexible sensor in personal health monitoring.

Antibacterial Efficacy and Surface Characteristics of Boron Nitride Coated Dental Implant: An In-Vitro Study.

This in vitro study evaluated bacterial cell proliferation and biofilm adhesion on titanium discs with and without antibacterial surface treatment to reduce the chances of peri-implant infections. Hexagonal boron nitride with 99.5% purity was converted to hexagonal boron nitride nanosheets via the liquid phase exfoliation process. The spin coating method was used for uniform coating of h-BNNSs over titanium alloy (Ti6Al4V) discs. Two groups of titanium discs were formed: Group I (n = 10) BN-coated titanium discs and Group II (n = 10) uncoated titanium discs. Two bacterial strains, Streptococcus mutans (initial colonizers) and Fusobacterium nucleatum (secondary colonizers), were used. A zone of inhibition test, microbial colony forming units assay, and crystal violet staining assay were used to evaluate bacterial cell viability. Surface characteristics and antimicrobial efficacy were examined by scanning electron microscopy with energy dispersion X-ray spectroscopy. SPSS (Statistical Package for Social Sciences) version 21.0 was used to analyze the results. The data were analyzed for probability distribution using the Kolmogorov-Smirnov test, and a non-parametric test of significance was applied. An inter-group comparison was done using the Mann-Whitney U test. A statistically significant increase was observed in the bactericidal action of BN-coated discs compared to uncoated discs against S. mutans, but no statistically significant difference was found against F. nucleatum.

Graphene Nanosheets Stabilized by P3HT Nanoparticles for Printable Metal-Free Electrocatalysts for Oxygen Reduction

The development of metal-free electrocatalysts with efficient catalytic performance and long-term stability is highly desirable for fuel cell applications. In this study, a solution-processable graphene-based electrocatalyst for the oxygen reduction reaction (ORR) is developed using a facile liquid-phase exfoliation process. An aqueous dispersion of poly(3-hexylthiophene-2,5-diyl) (P3HT) nanoparticles is prepared via a simple miniemulsion process and used as a medium for graphite exfoliation, where the interfacial interaction between P3HT nanoparticles and graphene is utilized to simultaneously stabilize the exfoliated graphene flakes and induce efficient intermolecular charge transfer to accelerate the ORR. Neutron scattering with contrast variation was carried out to study the colloidal architecture of the produced dispersions and the interactions at the interface between graphene and P3HT nanoparticles. The nanoparticle-stabilized graphene (G/P3HT) dispersions were employed for printing of flexible conductive circuits (∼180 Ω sq–1) and fabrication of metal-free electrocatalyst layers for the ORR, which reduces O2 molecules to OH– ions via the highly efficient four-electron pathway and exhibits superior stability (∼97% retention after 10,000 cycles). This printable graphene electrocatalyst provides a breakthrough in green chemistry and advanced techniques for the fabrication of low-cost and sustainable fuel cells.

Liquid-phase exfoliation of graphitic carbon nitrides studied by molecular dynamics simulation

HypothesisThe superiority of graphitic carbon nitride (g-C3N4) nanosheet results from its large specific surface area, which can be achieved by exfoliation of the bulk layered structure. Liquid-phase exfoliation (LPE) is the best-known method for the synthesis of two-dimensional (2D) g-C3N4 nanosheets. However, experimental investigations do not allow for a molecular-level understanding of the process. Molecular dynamics (MD) simulations are expected to provide microscopic insights and quantitative evaluation of the energy consumption during LPE, thus facilitating the search of effective solvents for the LPE of 2D materials. SimulationsMD simulations are carried out to simulate the LPE process by performing potential of mean force calculations for the separation of two stacked g-C3N4 nanosheets. Free energy of exfoliation is evaluated and compared among nine common solvents with distinct molecular structures. FindingsThe most probable path for the exfoliation process is identified. The free energy of exfoliation is found to correlate directly with the solvent free energy of a single g-C3N4 nanosheet. The solvation is enthalpy-driven and affected by the mobility of the solvent molecules around the nanosheet. Based on the MD results, several strategies are proposed to guide the selection of solvents for effective LPE.

Highly sensitive chemiresistive detection of NH3 by formation of WS2 nanosheets and SnO2 quantum dot heterostructures

The development of chemiresistive ammonia (NH3) sensors has attracted considerable attention for health monitoring applications. In this study, we fabricated two-dimensional (2D) tungsten disulfide (WS2) nanosheets decorated with tin oxide (SnO2) quantum dots for detecting NH3 gas. We tuned the WS2 nanosheet:SnO2 quantum dot ratio to achieve the maximum interfacial area to enhance the sensitivity of NH3 detection. First, the liquid-phase exfoliation process for WS2 was optimized to prepare a stable, high-concentration dispersion comprising 5–6 layers of WS2 nanosheets. Furthermore, SnO2 quantum dots interfaced with WS2 nanosheets at different ratios were prepared to fabricate NH3 sensors. The maximum response of the WS2/SnO2 heterostructure to 10 ppm NH3 was ∼850 % for a WS2:SnO2 ratio of 10:1, which exceeds the response of previously reported NH3 sensors. This superior response led to high sensitivity (∼175 % ppm−1) at low NH3 concentrations and a low limit of detection (∼10 ppb). The electron transfer at the WS2-SnO2 interface has been discussed by studying the bond formation between WS2 and SnO2 at different ratios. This insight into the sensing mechanism could be useful for the development of heterostructured sensors, which can be implemented for NH3 detection in industrial and medical fields.

A note on using expanded graphite for achieving energy‐ and time‐efficient production of graphene nanoplatelets via liquid phase exfoliation

AbstractAlthough easily scalable, the production of graphene nanoplatelets (GNP) by the means of liquid‐phase exfoliation of graphite flakes (GF) remains an energy‐ and time‐intensive process. In this work, we demonstrate that significant time and energy can be saved in GNP production when employing expanded graphite (EG) in a surfactant‐assisted liquid phase exfoliation process. Owing to its increased interlayer distance, the exfoliation of EG can be accomplished in a much shorter time (<30 min) compared to GF (approximately 7 h in the present case). Moreover, the energy required for the EG exfoliation is close to 80‐fold lower than that for GF exfoliation. Monitoring of the mean lateral dimension, specific surface area, and graphite flake‐to‐GNP transition during exfoliation was performed experimentally using several analytical techniques. The EG‐derived GNPs are produced much faster and require less energy for exfoliation compared to GF, thus making it a more efficient alternative technique.

Self-powered photodetector based on liquid phase exfoliated Cu–WSe2 nanosheets

According to its tuneable optoelectronic capabilities that enhanced the application of the photo-sensing device, the 2D-TMDC (transition metal dichalcogenides) deposited thin films have been the subject of additional research. Herein, we describe the high-quality crystalline behaviour of 10% incorporation of Cu in the pristine WSe2 nanosheets using two step liquid phase exfoliation process and its use as a broad range photodetector. The vapour phase technique is used to grown compounds. The elemental mapping and purity were analysed by EDAX. Powder Xray diffraction shows that all exfoliated nanosheets have a hexagonal lattice structure. The structural morphology was investigated by SEM and HR-TEM. The Raman Spectra reveal that the exfoliated nanosheets have in plane E2g vibration mode. The effect of alloy engineering on photo responsiveness has been investigated. The maximum photodetector parameters are examined for the ITO based Cu (10%) WSe2 photodetector under various wavelength dependent monochromatic light sources for 40 mW/cm2 power intensity.

Improved bioceramic coatings reinforced by nanostructured talc

Nano-talc was successfully incorporated in the hydroxyapatite matrix via pulsed electrodeposition after being obtained using an eco-friendly liquid-phase exfoliation process. Scanning electron microscopy, atomic force microscopy, X-ray spectroscopy, Raman spectroscopy, corrosion and wear resistance, and cytocompatibility tests were used to characterize the biocomposite ceramics. Talc significantly improves the nanomechanical and wear properties of bioceramics (i.e., higher stiffness, reduced friction coefficient, and lower wear damage) as well as corrosion resistance. Talc does not induce cytotoxic activity in in vitro cells and may induce bone maturation as per biocompatibility tests.

Highly sensitive and rapidly responding room-temperature NH3 gas sensor that is based on exfoliated black phosphorus

Black phosphorus (BP) has recently attracted significant interest in gas sensing because of its outstanding electronic and optical properties. In this paper, we demonstrated a series of gas sensors for detecting NH3 at room temperature that were based on BP nanosheets that were exfoliated for various durations. The BP nanosheet gas sensors showed excellent sensitivity for the detection of NH3 down to 100 ppb (~32%) under ambient conditions compared to previous reports. The BP nanosheets that were exfoliated for 60 min showed the highest response to 100 ppm NH3, namely, 121%, which was 2.5 times greater than the response of ground BP. The corresponding sensor also exhibited a relatively stable response in humidity between 22% RH and 35% RH. Moreover, the prepared NH3 gas sensor showed high selectivity, fast response and recovery, and excellent repeatability. According to various experimental and theoretical studies, the response and binding energy of BP towards NOx were higher than those towards NH3. However, very interestingly, the response of the exfoliated BP nanosheets to NH3 was higher than that to NOx in our work. The selectivity transformation from NOx to NH3 was mainly caused by the different layer spacing of the ground BP and the change in spacing between the BP nanosheet layers with different exfoliation times, increased oxygen incorporation, phosphate ions and defects that is induced by the liquid-phase exfoliation process, which led to the variations in its band gap and surface states.