Nguyen Duc Hoa

Hanoi University of Science and Technology (HUST) · International Training Institute for Materials Science (ITIMS)

The adverse effects of NO2 on the environment and human health promote the development of high-performance gas sensors to address the need for monitoring. Two-dimensional (2D) metal chalcogenides have been considered an emerging group of NO2-sensitive materials, while incomplete recovery and low long-term stability are the two major hurdles for the...

Gas sensors play an important role in many areas of human life, including the monitoring of production processes, occupational safety, food quality assessment, and air pollution monitoring. Therefore, the need for gas sensors to monitor hazardous gases, such as ammonia, at low operating temperatures has become increasingly important in many fields....

Recently, transition metal dichalcogenides (TMDs) have attracted much attention due to their high surface-to-volume ratio, various active edge sites, and adjustable bandgaps. However, in general, TMDs still exhibit low gas response and incomplete recovery. Surface modification is an effective way to facilitate the adsorption and desorption processe...

Nanohybrids, which comprise organic and inorganic materials, have gained increasing interest in the application for enhanced sensing response to both reducing and oxidation gases. In this study, we prepared nanohybrids of polyaniline (PANI) and ZnO nanoplates through a hydrothermal route for high-performance nitrogen dioxide gas sensing at low temp...

The air pollution caused by the emission of NO 2 from vehicles in large cities is threatening human health. Thus, a highly sensitive gas sensor is required to monitor this gas. Here, we introduced the arc-discharge deposition of single-walled carbon nanotubes (SWCNTs) over SnO 2 nanowires for highly sensitive NO 2 gas sensors. The high-quality SnO...

Many attempts have been made on the design and fabrication of low-power consumption gas sensor for application on the Internet of Things and portable devices. The performance of gas sensors includes sensitivity, selectivity, and power consumption, which are strongly dependent on the configuration of the device such as the gap size between two elect...

Gas sensor-embedded smartphones would offer the opportunity of on-site tracking of gas molecules for various applications, for example, harmful air pollutant alarms or noninvasive assessment of health status. Nevertheless, high power consumption and difficulty in replacing malfunctioned sensors as well as limited space in the smartphone to host the...

Two-dimensional (2D) metal sulfides have been an emerging material group for high-performance and power-saving gas sensing. However, relatively little attention is paid to developing doping-driven approaches to improve their gas interaction properties, particularly at room temperature. In this work, we realize room-temperature reversible NO2 gas se...

Metal oxides are ideal for the fabrication of gas sensors: they are sensitive to many gases while allowing the device to be simple, tiny, and inexpensive. Nonetheless, their lack of selectivity remains a limitation. In order to achieve good selectivity in applications with many possible interfering gases, the sensors are inserted into an electronic...

It is well-known that the amount of glucose in the blood that exceeds the normal sugar blood range can cause diabetes, which is one of the most dangerous diseases that thread human health. Amongst a lot of methods that have been developed to measure glucose levels, electrochemical glucose sensors have attracted more attention due to their accuracy...

Chemoresistive gas sensors play an important role in detecting toxic gases for air pollution monitoring. However, the demand for suitable nanostructures that could process high sensing performance remains high. In this study, hollow ZnO nanorices were synthesized by a simple hydrothermal method to detect NO2 and SO2 toxic gases efficiently. Materia...

Removal of carcinogenic Congo red from polluted water is challenging because of its chemical stability and inertness. Here, CuO microsphere assembled rGO nanosheets were successfully fabricated by a simple hydrothermal method for photocatalytic degradation of Congo red. The morphology and microstructure of the CuO/rGO nanocomposites were studied by...

Classification of different gases is important, and it is possible to use different gas sensors for this purpose. Electronic noses, for example, combine separated gas sensors into an array for detecting different gases. However, the use of separated sensors in an array suffers from being bulky, high-energy consumption and complex fabrication proces...

Features such as surface-to-volume ratio, sensitive surface, and bandgap vary with the number of material layers of semiconductor two-dimensional transition metal dichalcogenides with superior responsivity at room temperature (RT) and their possible application as flexible electronic devices. Herein, a significant enhancement of NO2 gas sensing pro...

In this study, ZnFe2O4 nanofibers were fabricated by facile electrospinning method and subsequent calcination process. The scanning electron microscopy (SEM) images showed that ZnFe2O4 nanofibers which were in diameters of 30-100 nm and consisted of nanograins had typical morphologies of spider nets. The X-ray diffraction (XRD) patterns revealed th...

Grafted structures between SnO2 and ZnO nanowires were realized in a two-step process of growth. First, the rootstocks of SnO2 or ZnO nanowires were synthesized by thermal evaporation technique. Second, a thin Au layer was sputter deposited on the sample and synthesis of nanowire scions of ZnO or SnO2, respectively, on the rootstocks was realized b...

Highly sensitive NO2 gas sensors with low detection limit are vital for practical application in air pollution monitoring. Here, the NO2 gas sensing performance of porous ZnO nanosheets and nanoplates were investigated, with different shape and thickness. It was found that ultra-thin ZnO nanoplates had a higher sensitivity than coral-like ZnO nanos...

Acetone in exhaled breath can be used as a biomarker for diabetes diagnosis, but its concentration is extremely low. Thus, a gas sensor with high sensitivity and a low detection limit (sub-ppm level) is vital in practical application. Here, ultrafine Pt nanoparticles were prepared and used to decorate the surface of Zn2SnO4 (ZTO) hollow octahedra f...

External and internal heterojunctions of reduced graphene oxide (rGO) and ZnO nanofibers (NFs) are developed for ultrasensitive H2S sensing. The gas response of both heterojunctions is significantly higher than that of bare ZnO NFs. The internal heterojunction of 0.1 wt.% rGO/ZnO NFs exhibited the highest gas response, reaching 1353 to 1 ppm H2S at...

People in developing countries are facing various fatal diseases like cancer, pneumonia, tuberculosis and especially diabetes due to the lack of low cost and effective diagnosis methods. Design and fabrication of effective materials for VOC gas sensor applications towards exhaled breath analysis in diabetic diagnosis is challenging because the gas...

A high working temperature of the ZnO nanomaterial-based gas sensor could shorten the lifetime of the sensor and increase its power consumption. Enhancing the VOC sensing performance of ZnO nanomaterials-based gas sensors in terms of gas response and temperature is vital for their practical application. Decoration of noble metals onto nanostructure...

In the current work, we report the on-chip fabrication of a low-temperature H₂S sensor based on p-type Co₃O₄ nanofibers (NFs) using the electrospinning method. The FESEM images show the typical spider-net like morphologies of synthesized Co₃O₄ NFs with an average diameter of 90 nm formed on the comb-like electrodes. The EDX data indicate the presen...

A unique combination of high response and fast response-recovery is still a challenge in the development of room-temperature gas sensors. Herein, we demonstrated the on-chip growth of nanojunction-networked SnO2 NW sensors to work under UV-radiation at room temperature. The morphological, compositional, and structural properties of synthesized SnO2...

The effect of MoS2 nanosheet (NS) decoration on the gas-sensing properties of SnO2 nanofibers (NFs) was investigated. The decorated sensors were fabricated by facile on-chip electrospinning technique and subsequently dropping MoS2 NSs-dispersed solution. The MoS2 NS decoration resulted in enhanced the response and reduced the operating temperature...

Because of the robustness and high catalytic activity of p-type CuO semiconducting nanostructures, they are applied as sensing materials for various gases. However, pristine CuO materials exhibit relatively low sensing performance to some gases, such as SO2 and H2. Here, we demonstrate an enhancement in the gas-sensing characteristics of CuO nanopl...

The enhancement of the H2S gas-sensing performance of SnO2 nanowires is vital for practical application. In this study, H2S gas sensors based on WO3-coated SnO2 nanowires were fabricated through a two-step process, namely, the chemical vapor deposition of SnO2 nanowires and then coating with WO3 by sputtering method. The morphology and crystal stru...

The design of hetero-nanojunctions can greatly amplify the gas-sensing performance of conventional metal oxide gas sensors. In this study, the composite nanofibers (NFs) of ZnO–SnO2 internal heterojunctions (HJs) and the mixed NFs of ZnO/SnO2 external HJs were realized by using the electrospinning technique. Then, the gas-sensing characteristics of...

The selective detection and classification of NH3 and H2S gases with H2S gas interference based on conventional SnO2 thin film sensors is still the main problem. In this work, three layers of SnO2/Pt/WO3 nanofilms with different WO3 thicknesses (50, 80, 140, and 260 nm) were fabricated using the sputtering technique. The WO3 top layer were used as...

Nanofibers of ZnO-SnO2 nanocomposites doped with Au crystals were synthesized by an electrospinning method for enhancement of H2S gas sensing performance. The mixed solution of zinc acetate dihydrate and tin(II) chloride dihydrate, dissolved in ethanol/DMF solvent, was spun directly on the interdigital Pt electrodes for sensor fabrication. Thermal...

Facile synthesis of advanced porous nanomaterials for enhanced gas sensing performance has gained increasing interest. Here, we report our study on the preparation of ultrathin porous ZnO nanoplates by a urea mediated hydrothermal method for acetone gas-sensor application. The synthesized ZnO nanomaterials were nanoplates with a porous structure, h...

We systematically investigated the effects of process conditions and reduced graphene oxide (RGO) loading on the H2S gas-sensing performance of the α-Fe2O3 nanofibers (NFs) fabricated via on-chip electrospinning. The annealing temperature and precursor solution contents strongly influenced on the morphology and structure of the α-Fe2O3 NFs that acc...

The monitoring and classification of different gases using a single resistive semiconductor sensor is challenging because of the similar response characteristics. An array of separated sensors can be used as an electronic nose, but such arrays have a bulky structure and complex fabrication processes. Herein, we easily fabricated a gas-sensor array...

SnO2 nanowires (NWs) are used in gas sensors, but their response to highly toxic gas H2S is low. Thus, their performance toward the effective detection of low-level H2S in air should be improved for environmental-pollution control and monitoring. Herein, Ag2O nanoparticle decorated SnO2 NWs were prepared by a simple on-chip growth and subsequent di...

We introduce a facile and scalable synthesis of rGO/WO3 nanocomposites by hydrothermal method for gas sensing applications. The characterization of rGO/WO3 nanocomposites by some advanced techniques such as scanning electron microscopy, high resolution transmission electron microscopy and Raman spectroscopy revealed that high quality rGO/WO3 nanoco...

In this work, four identical micro sensors on the same chip with noble metal decorated tin oxide nanowires as gas sensing material were located at different distances from an integrated heater to work at different temperatures. Their responses are combined in highly informative 4D points that can qualitatively (gas recognition) and quantitatively (...

In present work, we introduce the controlled synthesis of few layer vertically oriented MoS2 flakes for high performance NO2 gas sensor applications. The density and the thickness of MoS2 nanosheets are controlled by varying the heating rate of the chemical vapor deposition process. Our study confirms that the nanoflakes of about three layers were...

Fabrication of a high-performance room-temperature (RT) gas sensor is important for the future integration of sensors into smart, portable and Internet-of-Things (IoT)-based devices. Herein, we developed a NO2 gas sensor based on ultrathin MoS2 nanoflowers with high sensitivity at RT. The MoS2 flower-like nanostructures were synthesised via a simpl...

Monitoring of toxic gas in air is important because air pollution, especially in developing countries, has rapidly become severe. The high cost of installation and maintenance of a stationary analysis system by using methods such as gas chromatography limits its applications. Low-power, portable devices with relatively low-cost gas sensors are effe...

This study focuses on the synthesis of nanoporous NiO nanosheets hybridized with PEDOT:PSS, Cdot and Pt nanoparticles and screening the catalytic activities for the regeneration of iodide ions from triiodide ions in liquid-junction photovoltaic devices. Due to a special hexagonal structure of NiO nanosheets, Pt nanoparticles and Cdot are easily imm...

The monitoring and classification of different gases, such as H2 and NH3 using a low-cost resistive semiconductor sensor is preferred in practical applications in hydrogen energy, breath analysis, air pollution monitoring, industrial control, and etc. Herein, porous bi-layer Pt/SnO2 thin film sensors were fabricated to enhance H2 and NH3 sensing pe...

This work presents the synthesis of the transition metal oxides (micro‐wheels composed of self‐assembled WO3 nanorods, SnO2 nanosheets, and Fe2O3 nanoparticles) by hydrothermal method. The synthesized catalysts are then applied for the regeneration of iodide ions from triiodide ions at counter electrodes (CEs) of dye‐sensitized solar cells (DSCs)....

Two-dimensional porous ZnO nanosheets were synthesized by a facile hydrothermal method for ethanol gas-sensing application. The morphology, composition, and structure of the synthesized materials were characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, powder X-ray diffraction, and high-resolution transmission elect...

The synthesis of advanced functional nanomaterials for electrochemical applications, such as water splitting, dye-sensitized solar cells (DSCs), and supercapacitor has been the topic of interest in recent years. This work presents the synthesis of ruthenium (Ru)/reduced graphene oxide (RGO) nanocomposite by using a facile and scalable liquid plasma...

The study is aimed at investigating the stability of electrochemical and biosensing properties of ZnO nanorod-based platinum screen-printed electrodes (SPEs) applied for detection of bacterial pathogens. The platinum SPEs were designed and patterned according to standard photolithography and lift-off process on a silicon wafer. ZnO nanorods (NRs) w...

The highly toxic hydrogen sulphide (H 2 S) present in air can cause negative effects on human health. Thus, monitoring of this gas is vital in gas leak alarms and security. Efforts have been devoted to the fabrication and enhancement of the H 2 S-sensing performance of gas sensors. Herein, we used electron beam evaporation to decorate nickel oxide...

Developing metal oxide gas sensors for internet-of-things (IoT) and portable applications require low-power consumption because of the limited battery in devices. This requirement is challenging because metal oxide sensors generally need high working temperatures, especially for reducing gases. Herein, we present an effective design and fabrication...

In this study, we demonstrated two processes for the fabrication of thin films comprising ZnO nanocrystals dispersed in a SiO2 matrix doped with Er3+ ions (Er3+-doped SiO2/ZnO nanocomposites). The thin films can be applied as SiO2 glasses for optical waveguide materials working at the 1.54 μm band. In the first process, the conventional sol–gel met...

Room-temperature gas sensors are attracting attention because of their low power consumption, safe operation, and long-term stability. Herein, ZnO nanorods (NRs) and nanowires (NWs) were on-chip grown via a facile hydrothermal method and used for room-temperature NO 2 gas sensor applications. The ZnO NRs were obtained by a one-step hydrothermal pro...

Multisensor systems with low-power consumption are emerging for the Internet of Things. In this work, we demonstrate the use of self-heated networked Ag-decorated SnO 2 NW sensors integrated into a portable module for selective detection of H 2 S gas at low power consumption, and the integrated system is simulated as a virtual multisensor under var...

Cost-effective fabrication of sensors and detection of ultralow concentrations of toxic gases are important concerns for environmental monitoring. In this study, the reduced graphene oxide (RGO)-loaded ZnFe2O4 nanofibers (ZFO-NFs) were fabricated by facile on-chip electrospinning method and subsequent heat treatment. The multi-porous NFs with singl...

The long duration of a working device with a limited battery capacity requires gas sensors with low power consumption. A self-heated gas sensor is a highly promising candidate to satisfy this requirement. In this study, two gas sensors with sparse and dense SnO2 nanowire (NW) networks were investigated under the Joule heating effect at the nanojunc...

CuO nanoplates were synthesized by a facile hydrothermal method for a SO2 gas-sensing application. The synthesized materials were characterized by field-emission scanning electron microscopy (FE-SEM), powder x-ray diffraction (XRD), Raman spectroscopy, and photoluminescence spectroscopy. Gas-sensing characteristics were measured at various concentr...

In this work, we report on hydrothermal synthesis, structure, and photocatalytic properties of tin oxide/reduced graphene oxide (SnO2/rGO) nanocomposites with different GO concentrations. X-ray diffraction (XRD) patterns of the nanocomposites show the SnO2 tetragonal structure without the diffraction peaks of rGO phase. Field emission scanning elec...

ZnFe2O4 nanofiber gas sensors are cost-effectively fabricated by direct electrospinning on microelectrode chip with Pt interdigitated electrodes and subsequent calcination under different conditions to maximize their response to H2S gas. The synthesized nanofibers of approximately 30-100 nm in diameter show typical spider-net-like morphology of the...

Large-scale fabrication, sensitivity and selectivity are important considerations for the practical applications of metal-oxide nanowire (NW) gas sensors fabricated by thermal evaporation. This paper reports the effect of the distance between the source and the microelectronic chips on the gas-sensing properties of ZnO and Zn2SnO4 NW sensors fabric...

Understanding the formation mechanism and control of crystal evolution of nanoporous materials is important in the synthesis of nanoporous materials for enhanced gas-sensing performance. Herein, single crystal nickel hydroxide nanosheets were prepared by hydrothermal reaction between nickel chlorine and ammonium hydroxide. Then, the products were s...

Metal oxide nanostructures have been extensively used in electrochemical devices due to their advantages, including high active surface area and chemical stability. However, the electrochemical properties of metal oxides are strongly dependent on their structural characteristics. We performed a comparative study on the electrochemical performance o...

Hybrid heterojunction devices are designed for ultrahigh response to NO2 toxic gas. The devices were constructed by assembling multi-walled carbon nanotubes (MWCNTs) on a microelectrode chip bridged bare Pt-electrode and a Pt-electrode with pre-grown SnO2 nanowires (NWs). All heterojunction devices were realized using different types of MWCNTs, whi...

Synthesis of low cost, scalable, robust, and multifunctional nanomaterials for gas sensing application has been received increasing interest in recent years. Herein, we introduce the urea mediated synthesis of Ni(OH)2 nanowires and their conversion into NiO nanostructure for hydrogen gas-sensing application. The Ni(OH)2 nanowires were synthesized b...

ZnO nanostructures can be synthesized using different techniques for gas sensor applications, but different synthesis methods produce different morphologies, specific surface areas, crystal sizes, and physical properties, which consequently influence the gas-sensing properties of materials. Many parameters such as morphology, specific surface areas...

Three different ZnO nanostructures, dense nanorods, dense nanowires, and sparse nanowires, were synthesized between Pt electrodes by on-chip hydrothermal growth at 90°C and below. The three nanostructures were characterized by scanning electron microscopy and x-ray diffraction to identify their morphologies and crystal structures. The three ZnO nan...

Bilayer SnO2–WO3 nanofilm sensors with high sensitivity and selectivity for NH3 gas were developed. The sensitized WO3 nanofilms (5–15 nm) were deposited on the top of SnO2 nanofilms without vacuum break via reactive sputtering. The SnO2 nanofilm sensitized with 10-nm-thick WO3 nanofilm exhibited the best performance for sensing NH3 gas. The gas re...

In this study, we used a low-temperature hydrothermal technique to fabricate arrays of sensors with ZnO nanorods grown on-chip. The sensors on the glass substrate then were sputter decorated with Pd at thicknesses of 2, 4, and 8 nm and annealed at 650 °C in air for an hour. Scanning electron microscopy, high resolution transmission microscopy, X-ra...

The synthesis and integration of a compact, highly sensitive, and inexpensive gas sensor for breath analysis have attracted considerable attention because of painless application, non-invasiveness, and ability to diagnose diseases during early stages. In this study, we introduced the on-chip growth of SnO2 nanowire (NW)-based gas sensor to analyze...

The length of single crystalline nanowires (NWs) offers a perfect pathway for electron transfer, while small diameter of the NWs hampers losses to environment, substrate and metal electrodes. Therefore, Joule self-heating effect is nearly ideal for operating NW gas sensors at ultralow power consumption, without additional heaters. The realization o...

The local structure of single room- and high-temperature Co-implanted ZnO nanowires with subsequent thermal annealing has been studied using hard-x-ray techniques in combination with ab initio Zn K-edge x-ray absorption near-edge structure (XANES) simulations. X-ray fluorescence data reveal a homogeneous distribution of Co atoms/ions with concentra...

The morphology and crystalline size of metal oxide-sensing materials are believed to have a st