Insight into mechanism for remarkable photocatalytic hydrogen evolution of Cu/Pr dual atom co-modified TiO2.

The development of high-activity photocatalysts is crucial for the current large-scale development of photocatalytic hydrogen applications. Herein, we have developed a strategy to significantly enhance the hydrogen photocatalytic activity of Cu/Pr di-atom co-modified TiO2 architectures by selectively anchoring Cu single atoms on the oxygen vacancies of the TiO2 surface and replacing a trace of Ti atoms in the bulk with rare earth Pr atoms. Calculation results demonstrated that the synergistic effect between Cu single atoms and Pr atoms regulates the electronic structure of Cu/Pr-TiO2, thus promoting the separation of photogenerated carriers and their directional migration to Cu single atoms for the photocatalytic reaction. Furthermore, the d-band center of Cu/Pr-TiO2, which is located at -4.70 eV, optimizes the adsorption and desorption behavior of H*. Compared to TiO2, Pr-TiO2, and Cu/TiO2, Cu/Pr-TiO2 displays the best H* adsorption Gibbs free energy (-0.047 eV). Furthermore, experimental results confirmed that the photogenerated carrier lifetime of Cu/Pr-TiO2 is not only the longest (2.45 ns), but its hydrogen production rate (34.90 mmol g-1 h-1) also significantly surpasses those of Cu/TiO2 (13.39 mmol g-1 h-1) and Pr-TiO2 (0.89 mmol g-1 h-1). These findings open up a novel atomic perspective for the development of optimal hydrogen activity in dual-atom-modified TiO2 photocatalysts.

Changeable Active Sites by Pr Doping CuSA-TiO2 Photocatalyst for Excellent Hydrogen Production.

Photocatalytic water splitting for clean hydrogen production has been a very attractive research field for decades. However, the insightful understanding of the actual active sites and their impact on catalytic performance is still ambiguous. Herein, a Pr-doped TiO2-supported Cu single atom (SA) photocatalyst is successfully synthesized (noted as Cu/Pr-TiO2). It is found that Pr dopants passivate the formation of oxygen vacancies, promoting the density of photogenerated electrons on the CuSAs, and optimizing the electronic structure and H* adsorption behavior on the CuSA active sites. The photocatalytic hydrogen evolution rate of the obtained Cu/Pr-TiO2 catalyst reaches 32.88 mmol g-1 h-1, 2.3 times higher than the Cu/TiO2. Innovatively, the excellent catalytic activity and performance is attributed to the active sites change from O atoms to CuSAs after Pr doping is found. This work provides new insight for understanding the accurate roles of single atoms in photocatalytic water splitting.

Nonstoichiometric Doping of La0.9FexSn1-xO3 Hollow Microspheres for an Ultrasensitive Formaldehyde Sensor.

Oxygen vacancies play an essential role in gas-sensitive materials, but the intrinsic oxides are poorly controlled and contain low oxygen vacancy concentrations. In this work, we prepared La0.9Fe1-xSnxO3 microspheres with high sensitivity and controllability by a simple hydrothermal method, and then, we demonstrated that it has many oxygen ion defects by X-ray photoelectron spectroscopy and electron paramagnetic resonance characterization. The gas sensor exhibited ultrahigh response, specific recognition of formaldehyde gas, and excellent moisture resistance. By comparing the composites with different doping ratios, it was found that the highest catalytic activity was reached when x = 0.75, and the response value of La0.9Fe0.75Sn0.25O3 hollow microspheres at 200 °C reached 73-10 ppm of formaldehyde, which is 188% higher than that of intrinsic LaFeO3 hollow microspheres. On the one hand, due to the absence of A-site La3+ and the replacement of B-site Fe3+ by Sn4+, a large number of oxygen vacancies are induced on the surface and in the interior of the materials; on the other hand, it is also related to the large specific surface area and gas channels caused by the particular structure.

Surface Optics and Color Effects of Liquid Metal Materials.

Liquid metals (LMs) are emerging as new functional materials with rather unique physical or chemical behaviors. They are generally safe and nontoxic, have high boiling points, reflectivities, good thermal and electrical conductivities, flexibility, fluidity, self-healing capability and remain in liquid state at room temperature. However, the further applications of LMs are limited by their single-color physical appearance, such as working in the situations with imposed stringent requirements for color and aesthetics. Recently, the color and fluorescence functionalization of LMs have overcome many conventional technical bottlenecks and opened significant potential for emerging applications in numerous fields owing to their rich colors and unique liquid structure. In this review, the recent developments in the optical properties, color and fluorescence effects of LMs are comprehensively investigated. The synthesis, structures, properties, chromogenic mechanisms, and potential photoelectric applications of colorful LMs are systematically analyzed and compared. The effectiveness and characteristics of colorful LMs induced by coating, mixing, compounding, surface modification, external stimuli are provided, aiming to establish a potential system for the synthesis and practices of colorful LMs. Finally, the challenges and prospects in the field have also been identified and explained to preferably guide further scientific and technical research in the coming time.

Excellent performance supercapacitors with the compounding of Ni(OH)2 and ZIF-67 derived Co-C-N nanosheets as flexible electrode materials.

Owing to the advantages of high theoretical capacity, low cost, and excellent chemical stability, Ni(OH)2 is considered as a potential candidate for electrode materials of supercapacitors. However, its further applications are limited by its adverse surface chemical properties. In this paper, a composite material consisting of ZIF-67 derived Co-C-N nanosheets and Ni(OH)2 was synthesized facilely on carbon cloth in situ, and based on the collective advantages of the various components, excellent electrochemical performance could be achieved when used as a flexible electrode material of supercapacitors. In detail, the as-obtained sample Ni(OH)2/Co-C-N/CC exhibits an ultrahigh specific capacitance of 2100 F g-1 at a current density of 1 A g-1. Moreover, the further assembled asymmetric supercapacitor device exhibits a maximum energy density of 78.6 W h kg-1 at a power density of 749.4 W kg-1. Furthermore, the device also shows outstanding cycling stability with 90.2% capacitance retention after 5000 cycles of charge-discharge. Basically, the remarkable performance can be attributed to the well-developed structure, abundant active sites, complex beneficial components, and their intrinsic properties. Significantly, rational design can broaden the research directions of corresponding electrode materials.

Pd-SnO2/In2O3 with a Unique Structure for the Ultrasensitive Detection of Triethylamine near Room Temperature.

Triethylamine (TEA) is a serious threat to people's health, and it is still a challenge to detect TEA at ppb level near room temperature (RT). Herein, we developed a simple, low-cost, low-temperature, and ultra-sensitive TEA sensor based on Pd-SnO2/In2O3 composites. First, SnO2 nanoparticles were obtained by the pyrolysis of Sn-MOF@SnO2 precursor (MOF: metal organic framework), and Pd-SnO2/In2O3 composites were prepared by further compounding and doping. The results show that the Pd-SnO2/In2O3 sensor is highly sensitive to TEA gas at near RT (at 60 °C, the sensor response to 10 ppm TEA is 12,000, the response/recovery (res/rec) time is 51 s/493 s, and at 30 °C, the response value also reaches 1380, the res/rec time is 66 s/610 s), along with good selectivity, stability, and moisture resistance. Even at 10 °C operating temperature and 75% relative humidity (RH) in a low-temperature and high-humidity environment, it still maintains a high sensitivity of over 1000 to 10 ppm TEA, which shows great application potential in TEA detection. The reason for the enhanced performance of the 0.5%Pd-SnO2/In2O3 sensor can be attributed to a large number of adsorbed oxygens on the unique structure of the material, the good charge transfer ability of the n-n-type heterojunction between SnO2 and In2O3, the chemical sensitization and electronic sensitization of Pd nanoparticles, and the catalytic spillover effect. This work will provide a new approach for preparing sensors with good comprehensive properties, making full use of the advantages of the material structure-activity relationship.

Highly sensitive triethylamine gas sensor by Pt-loaded p-n heterojunction Co3O4/WO3.

Triethylamine (TEA) exists widely in production and life and is extremely volatile, which seriously endangers human health. It is required to develop high-performance TEA sensors to protect human health. We fabricated Pt-Co3O4/WO3based on our previous work, and the performance was tested against volatile organic compounds. Compared with the previous work, its operating temperature was greatly reduced from 240 °C to 180 °C. The response value of Pt-Co3O4/WO3was increased from 1101 to 1532 for 10 ppm TEA with good selectivity. These results show a significant step toward practical use of the Pt-Co3O4/WO3sensor.

Ultrasensitive Formaldehyde Sensor Based on SnO2 with Rich Adsorbed Oxygen Derived from a Metal Organic Framework.

SnO2 has been a commonly researched gas-sensing material due to its low cost, good performance, and good stability. However, gas sensors based on pure SnO2 usually show a low response or high working temperature. In this work, laminar SnO2 was obtained by using a Sn-based metal organic framework(Sn-MOF)@SnO2 as a precursor. Sn-MOF@SnO2 is prepared at low temperatures using water and dimethylformamide as a solvent, which is simple, low cost, and easily reproducible. After sintering, Sn-MOF@SnO2 is derived to SnO2 with rich adsorbed oxygen, large specific surface area, and unique nanoparticle piled pores, thus showing excellent gas-sensing properties. The prepared SnO2 has an ultrahigh response value of 10,000 to 10 ppm formaldehyde at an optimal working temperature of 120 °C, a fast response/recovery time of 33 s/142 s, and an actual detection limit of lower than 10 ppb as well as high selectivity and high stability. Density functional theory calculations show that the exposed (110) plane of oxygen-rich vacancies in laminar SnO2 can effectively increase the coadsorption capacity of O2 and formaldehyde molecules, thereby improving the formaldehyde gas-sensing performance of the material. The present original approach paves the way to design advanced materials with excellent gas-sensing properties as well as broad application prospects in formaldehyde monitoring.

Formaldehyde gas sensor with extremely high response employing cobalt-doped SnO2 ultrafine nanoparticles.

Formaldehyde is a common carcinogen in daily life and harmful to health. The detection of formaldehyde by a metal oxide semiconductor gas sensor is an important research direction. In this work, cobalt-doped SnO2 nanoparticles (Co-SnO2 NPs) with typical zero-dimensional structure were synthesized by a simple hydrothermal method. At the optimal temperature, the selectivity and response of 0.5% Co-doped SnO2 to formaldehyde are excellent (for 30 ppm formaldehyde, R a/R g = 163 437). Furthermore, the actual minimum detectable concentration of 0.5%Co-SnO2 NPs is as low as 40 ppb, which exceeds the requirements for formaldehyde detection in the World Health Organization (WHO) guidelines. The significant improvement of 0.5%Co-SnO2 NPs gas performance can be attributed to the following aspects: firstly, cobalt doping effectively improves the resistance of SnO2 NPs in the air; moreover, doping creates more defects and oxygen vacancies, which is conducive to the adsorption and desorption of gases. In addition, the crystal size of SnO2 NPs is vastly small and has unique physical and chemical properties of zero-dimensional materials. At the same time, compared with other gases tested, formaldehyde has a strong reducibility, so that it can be selectively detected at a lower temperature.

Silver nanoparticles embedded 2D g-C3N4nanosheets toward excellent photocatalytic hydrogen evolution under visible light.

Photocatalytic water splitting is considered to be a feasible method to replace traditional energy. However, most of the catalysts have unsatisfactory performance. In this work, we used a hydrothermal process to grow Ag nanoparticlesin situon g-C3N4nanosheets, and then a high performance catalyst (Ag-g-C3N4) under visible light was obtained. The Ag nanoparticles obtained by this process are amorphous and exhibit excellent catalytic activity. At the same time, the local plasmon resonance effect of Ag can effectively enhance the absorption intensity of visible light by the catalyst. The hydrogen production rate promote to 1035µmol g-1h-1after loaded 0.6 wt% of Ag under the visible light, which was 313 times higher than that of pure g-C3N4(3.3µmol g-1h-1). This hydrogen production rate is higher than most previously reported catalysts which loaded with Ag or Pt. The excellent activity of Ag-g-C3N4is benefited from the Ag nanoparticles and special interaction in each other. Through various analysis and characterization methods, it is shown that the synergy between Ag and g-C3N4can effectively promote the separation of carriers and the transfer of electrons. Our work proves that Ag-g-C3N4is a promising catalyst to make full use of solar energy.

Pt Single Atom-Induced Activation Energy and Adsorption Enhancement for an Ultrasensitive ppb-Level Methanol Gas Sensor.

As an important organic chemical raw material, methanol is used in various industries but is harmful to human health. Developing an effective and accurate detection device for methanol is an urgent need. Herein, we demonstrate a novel gas-sensing material with a Pt single atom supported on a porous Ag-LaFeO3@ZnO core-shell sphere (Ag-LaFeO3@ZnO-Pt) with a high specific surface area (192.08 m2·g-1). Based on this, the surface activity of the Ag-LaFeO3@ZnO-Pt gas sensor is enhanced obviously, which improved the working temperature and detection limit for methanol gas. Consequently, this sensor possesses an ultrahigh sensitivity of 453.02 for 5 ppm methanol gas at a working temperature of 86 °C and maintains a high sensitivity of 21.25 even at a concentration as low as 62 ppb. The sensitivity of Ag-LaFeO3@ZnO-Pt to methanol gas is increased by 6.69 times compared with the Ag-LaFeO3@ZnO core-shell sphere (Ag-LaFeO3@ZnO). Additionally, the minimum detection limit is found to be 3.27 ppb. Detailed theoretical calculations revealed that the unoccupied 5d state of Pt single atoms increases the adsorption and activation energy of methanol and oxygen, which facilities methanol gas-sensing performance. This work will provide a novel strategy to design high-performance gas-sensing materials.

Ultrasensitive ppb-level trimethylamine gas sensor based on p-n heterojunction of Co3O4/WO3.

Trace poisonous and harmful gases in the air have been harming and affecting people's health for a long time. At present, effective and accurate detection of ppb-level harmful gas is still a bottleneck to be overcome. Herein, we report a ppb-level triethylamine (TEA) gas sensor based on p-n heterojunction of Co3O4/WO3, which is prepared with ZIF-67 as the precursor and provides Co3O4deposited tungsten oxide flower-like structure. Due to the introduction of Co3O4and the 3D flower-like structure of WO3, the Co3O4/WO3-2 gas sensor shows excellent gas sensing performance (1101 for 10 ppm at 240 °C), superb selectivity, good long-term stability and linear response for TEA concentration. Moreover, the experimental results indicate that the Co3O4/WO3-2 gas sensor also possesses a good response to 50 ppb TEA, in fact, the theoretical limit of detection is 0.6 ppb. Co3O4not only improves the efficiency of electron separation/transport, but also accelerates the oxidation rate of TEA. This method of synthesizing p-n heterojunction with ZIF as the precursor provides a new idea and method for the preparation of low detection limit gas sensors.

Gas sensing materials roadmap.

Gas sensor technology is widely utilized in various areas ranging from home security, environment and air pollution, to industrial production. It also hold great promise in non-invasive exhaled breath detection and an essential device in future internet of things. The past decade has witnessed giant advance in both fundamental research and industrial development of gas sensors, yet current efforts are being explored to achieve better selectivity, higher sensitivity and lower power consumption. The sensing layer in gas sensors have attracted dominant attention in the past research. In addition to the conventional metal oxide semiconductors, emerging nanocomposites and graphene-like two-dimensional materials also have drawn considerable research interest. This inspires us to organize this comprehensive 2020 gas sensing materials roadmap to discuss the current status, state-of-the-art progress, and present and future challenges in various materials that is potentially useful for gas sensors.

Hybrid cobalt-manganese oxides prepared by ordered steps with a ternary nanosheet structure and its high performance as a binder-free electrode for energy storage.

Binder-free electrodes for supercapacitors have attracted much attention as no additive is required in their preparation processes. Herein, a hybrid metal oxide composed of graphene oxide (Co3O4/MnO2/GO) was successfully prepared. Briefly, electrochemical deposition and sintering were applied to grow Co3O4 nanosheets on nickel foam. Subsequently, MnO2 nanosheets were deposited on Co3O4 nanosheets via the thermal decomposition of a KMnO4 aqueous solution. Finally, graphene oxide was added to improve the performance of the composite. Particularly, the as-obtained Co3O4/MnO2/GO sample grown on nickel foam possessed a ternary nanosheet structure, and when applied as a binder-free electrode in a supercapacitor, it exhibited an excellent electrochemical performance. Firstly, the electrode exhibited an ultrahigh capacitance value of 2928 F g-1 at 1 A g-1 in a three-electrode system. Besides, the electrode showed a promising rate performance of 853 F g-1 at a high current density of 20 A g-1. Moreover, the electrode displayed a relatively high energy density of 97.92 W h kg-1 at a power density of 125 W kg-1 and long cycle life of 93% retention after 5000 cycles at 10 A g-1 in a two-electrode system. Thus, all the electrochemical tests suggest that the Co3O4/MnO2/GO binder-free electrode is a potential candidate for energy storage.

Platinum-Supported Cerium-Doped Indium Oxide for Highly Sensitive Triethylamine Gas Sensing with Good Antihumidity.

Triethylamine is extremely harmful to human health, and chronic inhalation can lead to respiratory and hematological diseases and eye lesions. Hence, it is essential to develop a triethylamine gas-sensing technology with high response, selectivity, and stability for use in healthcare and environmental monitoring. In this work, a simple and low-cost sensor based on the Pt- and Ce-modified In2O3 hollow structure to selectively detect triethylamine is developed. The experimental results reveal that the sensor based on 1% Pt/Ce12In exhibits excellent triethylamine-sensing performance, including its insusceptibility to water, reduced operating temperature, enhanced response, and superior long-term stability. This work suggests that the enhancement of sensing performance toward triethylamine can be attributed to the high relative contents of OV and OC, large specific surface area, catalytic effect, the electronic sensitization of Pt, and the reversible redox cycle properties of Ce. This sensor represents a unique and highly sensitive means to detect triethylamine, which shows great promise for potential applications in food safety inspection and environmental monitoring.

Microwave-assisted synthesis of porous and hollow α-Fe2O3/LaFeO3 nanostructures for acetone gas sensing as well as photocatalytic degradation of methylene blue.

To address the urgent issues of hazardous gas detection and the prevention of environmental pollution, various functional materials for gas sensing and catalytic reduction have been studied. Specifically, the p-type perovskite LaFeO3 has been studied widely because of its promising physicochemical properties. However, there remains several problems to develop a controllable synthesis of LaFeO3-based p-n heterojunctions. In this work, α-Fe2O3 was further compounded with LaFeO3 to form a porous and hollow α-Fe2O3/LaFeO3 heterojunction to improve its gas-sensing performance and photocatalytic efficiency via a microwave-assisted hydrothermal method. While evaluated as sensors of acetone gas, the optimized sample exhibits excellent performance, including a high response (48.3), excellent selectivity, good reversibility, fast response, and recovery ability. Furthermore, it is an efficient catalyst for the degradation of methylene blue. This can be attributed to the enhancement effect of its larger specific surface area, fast diffusion, enhanced surface activities, and p-n heterojunction. Additionally, this work provides a rapid and rational synthesis strategy to produce metal oxides with both enhanced gas-sensing performance and improved photocatalytic properties.

Highly selective and sensitive methanol gas sensor based on molecular imprinted silver-doped LaFeO3 core-shell and cage structures.

Silver-doped LaFeO3 molecularly imprinted polymers (SLMIPs) were synthesized by a sol-gel method combined with molecularly imprinted technology as precursors. The precursors were then used to prepare SLMIPs cage (SLM-cage) and SLMIPs core-shell (SLM-core-shell) structures by using a carbon sphere as the template and hydrothermal synthesis, respectively. The structures, morphologies, and surface areas of these materials were determined, as well as their gas-sensing properties and related mechanisms. The SLM-cage and SLM-core-shell samples exhibited good responses to methanol gas, with excellent selectivity. The response and optimum working temperature were 16.98 °C and 215 °C, 33.7 °C and 195 °C, respectively, with corresponding response and recovery times of 45 and 50 s (SLM-cage) and 42 and 57 s (SLM-core-shell) for 5 ppm methanol gas. Notably, the SLM-cage and SLM-core-shell samples exhibited lower responses (≤5 and ≤7, respectively) to other gases, including ethanol, ammonia, benzene, acetone, and toluene. Thus, these materials show potential as practical methanol detectors.