Two-step Hydrothermal Method Research Articles

Zn-doped CdSSe composite quantum dots synthesized by a two-step hydrothermal ion exchange in sensitized solar cells

Metal ion doping is an effective strategy for enhancing the photoelectric properties of quantum dots (QDs). In this study, Zn-doped CdSSe composite QDs (ZnCdSSe) were synthesized using a two-step hydrothermal ion exchange method. The synthesis process involved the exchange reaction of Cd2+ with Zn2+, followed by the exchange reaction of Se2− with S2−, based on ZnS templates. The morphology, composition and crystalline phase of synthesized QDs were characterized using X-ray and electron-based techniques such as XRD, SEM, TEM, and XPS. The results indicate ZnCdSSe QDs were synthesized while preserving a similar morphology to that of ZnCdS. Performance tests demonstrated that quantum dot sensitized solar cells (QDSSCs) equipped with ZnCdSSe/TiO2 photoanodes achieved a power conversion efficiency (PCE) of 3.61% by optimizing the hydrothermal reaction temperature and time. This efficiency was 33.2% higher than that of CdSSe (2.17%) QDSSCs synthesized via a one-step hydrothermal exchange reaction using CdS templates. The significant enhancement in PCE can be attributed to improvements in light absorption and charge carrier transport. Notably, Zn doping reduced interface charge recombination and prolong electronic lifetime (τn), facilitating more effective charge collection in QDSSCs.

Designed Synthesized Step-Scheme Heterojunction of Bi2WO6 Nanosheet Supported on CuBi2O4 Nanorod with Remarkable Photo-assisted Gas Sensing for N-butyl alcohol

Photo-assisted gas sensors for n-butyl alcohol detection have attracted considerable attention due to their great potential in safety production and human health. However, the sensitivity, selectivity and stability should be further improved for practical application. Herein, Bi2WO6 nanosheet supported on CuBi2O4 nanorod sensor was realized by the two-step hydrothermal method, and it exhibited excellent sensitivity and stability for n-butyl alcohol detection under blue LED light illumination at the operating work temperature of 110oC with gas concentration from 0.5 to 800 ppm. Meanwhile, the gas concentration of n-butyl alcohol obtained from the sensor was comparable to that of GC analysis. Furthermore, the sensor showed lower responses to other 25 kinds of common organic gases including alcohols, aldehydes, benzenes and ketones compared with that of n-butyl alcohol. More attractively, the Bi2WO6/CuBi2O4 sensor maintained its stable photo-assisted sensing activity over 3 months. The excellent gas-sensing property was caused by light illumination and formation of Bi2WO6/CuBi2O4 heterojunction, leading to abundant active electrons and superoxide radicals. The S-scheme mode of charge transfer at the Bi2WO6/CuBi2O4 heterojunction was revealed by the in-situ XPS and in-situ ESR analyses. The results gained herein may be useful for rational design of S-scheme heterojunction in photo-assisted gas sensor for n-butyl alcohol analysis.

Tuning Electrons Migration of Dual S Defects Mediated MoS2-x/ZnIn2S4-x Toward Highly Efficient Photocatalytic Hydrogen Production.

Photocatalytic hydrogen production is a prevalent method for hydrogen synthesis. However, high recombination rate of photogenerated carriers and high activation energy barrier of H remain persistent challenge. Here, the two-step hydrothermal method is utilized to prepare dual S-defect mediated catalyst molybdenum sulfide/zinc indium sulfide (MSv/ZISv), which has high hydrogen production rate of 8.83 mmolg-1h-1 under simulated sunlight. The achieved rate is 21.91 times higher than pure ZnIn2S4 substrate. Defects in ZIS within MSv/ZISv modify the primitive electronic structure by creating defect state that retaining good reducing power, leading to the rapid separation of electron-hole pairs and the generation of additional photogenerated carriers. The internal electric field further enhances the migration toward to cocatalyst. Simultaneously, the defects introduced on the MoS2 cause electron rearrangement, leading to electron clustering on both S vacancies and edge S. Thereby MSv/ZISv exhibits the lowest activation energy barrier and |ΔGH*|. This work explores the division of synergies between different types of S defects, providing new insights into the coupling of defect engineering.

Porphyrin functionalized montmorillonite Loaded Cu2O-Fe3O4 as a sustainable peroxidase nanozyme for colorimetric determination of hydroquinone

Designing sustainable efficient peroxidase nanozymes and elucidating its peroxidase-like mechanism are very important for constructing colorimetric sensing platforms. Herein, a sustainable peroxidase nanozyme, porphyrin functionalized montmorillonite (PorMMT) loaded Cu2O-Fe3O4 nanocomposites, is prepared by the two-step hydrothermal method and can be recycled conveniently by virtue of magnetism of Fe3O4 from the composite (Cu2O-Fe3O4/PorMMT). Cu2O-Fe3O4/PorMMT peroxidase nanozyme can quickly catalyze the oxidation of the colourless substrate 3,3′,5,5′-tetramethylbiphenylamine (TMB) by H2O2 into a blue product (oxTMB) only in 3 min. Compared with pure MMT, Cu2O and Fe3O4 individual, Cu2O-Fe3O4/PorMMT exhibits the higher peroxidase-like activity. The catalytic activity of Cu2O-Fe3O4/PorMMT is reached the maximum at pH = 4 and T = 50 ℃. The catalytic behaviors of Cu2O-Fe3O4/PorMMT follow the Michaelis-Menten kinetic equation. The catalytic mechanism of Cu2O-Fe3O4/PorMMT is from the produced active species including superoxide free radicals (•O2−) and holes (h+). Based on the peroxidase-like activity of Cu2O-Fe3O4/PorMMT, a fast convenient colorimetric sensing platform has been designed to detect H2O2 and hydroquinone (HQ), respectively. H2O2 detection can be realized in the linear range of 510 mM with the limit of detection (LOD) of 2.68 mM, as well as hydroquinone (HQ) in the linear range of 550 μM with a much lower LOD of 4.37 μM. The convenient visual sensing platform has a potential application in monitoring HQ remains in lakes and rivers near dressing plants.

A binary dumbbell visible light driven photocatalyst for simultaneous hydrogen production with the selective oxidation of benzyl alcohol to benzaldehyde

Photocatalytic H2 production with selective oxidation of organic moieties in an aqueous medium is a fascinating research area. However, the rational design of photocatalysts and their photocatalytic performance are still inadequate. In this work, we efficiently synthesized the MoS2 tipped CdS nanowires (NWs) photocatalyst using soft templates via the two-step hydrothermal method for efficient H2 production with selective oxidation of benzyl alcohol (BO) under visible light illumination. The optimized MoS2 tipped CdS NWs (20 % MoS2) photocatalyst exhibits the highest photocatalytic H2 production efficiency of 13.55 mmol g−1 h−1 with 99 % selective oxidation of BO, which was 42.34 and 2.21 times greater photocatalytic performance than that of pristine CdS NWs and MoS2/CdS NWs, respectively. The directional loading of MoS2 at the tips of CdS NWs (as compared to nondirectional MoS2 at CdS NWs) is the key factor towards superior H2 production with 99 % selective oxidation of BO and has an inhibitory effect on the photo corrosion of pristine CdS NWs. Therefore, the amazing enhancement in the photocatalytic performance and selectivity of optimized MoS2 tipped CdS NWs (20 % MoS2) photocatalyst is due to the spatial separation of their photoexcited charge carriers through the Schottky junction. Moreover, the unique structure of the MoS2 flower at the tip of 1D CdS NWs offers separate active sites for adsorption and surface reactions such as H2 production at the MoS2 flower (confirmed by Pt photo deposition) and subsequently the selective oxidation of BO at the stem of CdS NWs. This rational design of a photocatalyst could be an inspiring work for the further development of an efficient photocatalytic system for H2 production with selective oxidation of BO (a strategy of mashing two potatoes with one fork).

Robust Superhydrophobic Composite Fabric with Self-Healing and Chemical Durability.

Superhydrophobic fabrics with multiple functions have become a research hotspot. However, it is challenging to make self-healing mechanically robust and eco-friendly superhydrophobic fabrics, which are limited by complex fabrication processes and excessive use of environmentally unfriendly solvents during fabrication. Herein, inspired by the secretion of a waxy substance from the surface of lotus leaves to restore water repellency, self-healing superhydrophobic composite fabrics (as-synthesized PA66/6-PET@Tico) are obtained by constructing a papillary TiO2 and tentacle-like fluorinated acrylate polymer (FCB015) coating on polyester-nylon composite fabrics using two-step hydrothermal method. The result indicates that PA66/6-PET@Tico with hierarchical micro/nanostructure exhibits excellent superhydrophobic and self-healing properties. Compared with FCB015 coated fabric, the contact angles (CA) of water and soybean oil rise to 172.2° and 166.8° from 137.4° and 98.8°, respectively. After mechanical abrasion, PA66/6-PET@Tico recovers a water contact angle (WCA) of 165.6° at room temperature. The WCA remains higher than 155° after 18h of chemical corrosion. Furthermore, the bacterial inhibition rates of PA66/6-PET@Tico for Staphylococcus Aureus and Escherichia Coli are 99.90 and 98.38%, respectively. In this work, a new idea is proposed for designing a simple and effective self-healing superhydrophobic coating, expecting to promote the large-scale industrial production and application of functional surfaces.

MoS2-CuCo2S4 nanosheets with a honeycomb structure formed on Ni foam: An efficient electrocatalyst for hydrogen evolution reaction

The physical, chemical, and electrocatalytic properties of conventional single-component electrocatalysts developed for the hydrogen evolution reaction (HER) no longer match the needs of many commercial applications. This necessitates for the creation of more sophisticated and effective electrocatalysts for the HER. In this study, MoS2-CuCo2S4 was loaded onto NF using a simple two-step hydrothermal method. In the resultant NF/MoS2-CuCo2S4 material, CuCo2S4 offers a lot of active sites to support vertically arranged MoS2 nanosheets, thereby decreasing their agglomeration. Moreover, the heterogeneous structure formed between CuCo2S4 and MoS2 facilitates charge transfer and exposes the active sites for HER, further improving the electrochemical hydrogen evolution performance of the heterostructured electrocatalyst. In a 1.0 M KOH solution, the synthesized NF/MoS2-CuCo2S4 nanosheet catalyst has outstanding electrocatalytic efficacy, with an overpotential as low as 67 mV at a current density of 10 mA·cm−2.

Photocatalysis Meets Piezoelectricity in a Type-I Oxygen Vacancy-Rich BaTiO3/BiOBr Heterojunction: Mechanism Insights from Characterizations to DFT Calculations.

It is a challenging task to design a piezoelectric photocatalyst with excellent performance under mechanical agitation instead of ultrasonic irradiation. Integrating vacancy defects into a heterojunction seems to be an effective strategy for synergistically increasing its piezo-photocatalytic performance. For this goal, a two-step hydrothermal method was adopted to architect a type-I oxygen-vacancy-rich BaTiO3/BiOBr heterojunction to surge the degradation of Rhodamine B (RhB) under the combined action of simulated sunlight irradiation and mechanical agitation. Various instrumental techniques demonstrated the formation of a BaTiO3/BiOBr heterojunction with high crystallinity. The existence of surface oxygen vacancies was confirmed by XPS and EPR tests. PFM results manifested that this heterojunction had excellent piezoelectric properties, with a piezoelectric response value of 30.31 pm V-1. Comparative experiments indicated that RhB degradation efficiency under piezo-photocatalysis over this heterojunction largely exceeded the total sum of those under piezocatalysis and photocatalysis. h+, ·O2-, and 1O2 were the dominant reactive species for RhB degradation. The improved separation efficiency of photogenerated charges was verified by electrochemical measurements. DFT calculations indicated that the polarization of BaTiO3 could affect the electronic band structure of BiOBr. This work will provide comprehensive insights into piezo-photocatalytic mechanism at a microcosmic level and help to develop new-styled piezoelectric photocatalysts.

Strong Carbon Layer-Encapsulated Cobalt Tin Sulfide-Based Nanoporous Material as a Bifunctional Electrocatalyst for Zinc-Air Batteries.

Global demands for cost-effective, durable, highly active, and bifunctional catalysts for metal-air batteries are tremendously increasing in scientific research fields. In this work, a strategy for the rational fabrication of carbon layer-encapsulated cobalt tin sulfide nanopores (CoSnOH/S@C NPs) material as a bifunctional electrocatalyst for rechargeable zinc (Zn)-air batteries by a cost-effective and facile two-step hydrothermal method is reported. Moreover, the effect of metal elements on the morphology of CoSnOH nanodisks material via the hydrothermal method is investigated. Owing to its excellent nanostructure, exclusive porous network, and high specific surface area, the optimized CoSnOH/S@C NPs material reveals superior catalytic properties. The as-prepared CoSnOH/S@C NPs electrocatalyst reveals better properties of oxygen reduction reaction (half-wave potential of -0.88 V vs reversible hydrogen electrode) and oxygen evolution reaction (overpotential of 137mV at 10mAcm-2) when compared with commercial Pt/C and IrO2 catalyst materials. Most significantly, the CoSnO/S@C NPs-based Zn-air battery exhibits more excellent cycling stability than the Pt/C+IrO2 catalyst-based one. Consequently, the proposed material provides a new route for fabricating more active and stable multifunctional catalyst materials for energy conversion and storage systems.

Synthesis of millimetre-scale HZSM-5 single crystals by secondary hydrothermal treatment

Millimetre-scale HZSM-5 single crystals were successfully synthesized by a two-step hydrothermal method. In the first step, millimetre-sized silicalite-1 single crystals were prepared by hydrothermal synthesis using quartz tube as siliceous source. In the second step, framework Al atoms were inserted into the single crystals of silicalite-1 by another hydrothermal treatment involving NaAlO2 as aluminium source. Through the characterizations of power and single crystal X-ray diffraction, optical microscope, ICP, 27Al MAS NMR, 29Si MAS NMR, and n-propylamine temperature-programmed decomposition (NPA-TPD), it was confirmed framework Al atoms with uniform spatial distribution can be inserted into giant single crystals of silicalite-1 with no obvious effects on the crystal structure, size and morphology. Such giant HZSM-5 single crystals are a promise candidate for the probe adsorption investigations, which can be applied in the measurement of framework Al spatial distribution. The strategy of insertion of aluminium or other heteroatoms of pure siliceous zeolite through secondary hydrothermal method provides a possible route to prepare giant single crystals that is difficult to synthesize directly.

Highly responsive and swift recovery triethylamine gas sensor based on NiCo2O4-ZnO p-n heterojunction

In the detection of food freshness and chemical production, live tracking of the concentration of triethylamine gas is both essential and challenging. The NiCo2O4-ZnO triethylamine gas sensor prepared with two-step hydrothermal method proposed in this study exhibits a response of TEA at the ideal operational temperature of 250 °C and a response/recovery time of 69 s/2 s. Compared to the single ZnO sensor, the response value is increased by a factor of 8.47, the recovery time is reduced to 1/8, and good selectivity (the response for TEA is 4.75 times higher than others), repeatability, and long-term stability (40 days) are demonstrated. Notably, research on fabricating TEA gas sensors by constructing p-n heterojunctions using NiCo2O4 and ZnO composites is currently lacking. The enhancement of the gas-sensitive properties of the composites is the result of a combination of factors such as increased specific surface area (18.18 m2/g−1) and pore size (29.84 nm), the formation of p-n heterojunctions, and the synergistic effect between the two materials. The excellent TEA sensitivity exhibited by the NiCo2O4-ZnO composites holds considerable practical application potential in triethylamine gas sensors.

Hierarchical CoWO4/NixFeyS microspheres bearing crystalline-amorphous interface as a multifunctional platform for outperformed water splitting and sensitive hydrazine sensing

Highly efficient and multifunctional electrocatalysts are of high value in energy transformation and electrochemical sensing. Herein, hierarchically architectured cobalt tungstate/nickel iron sulfide (CoWO4/NixFeyS) microspheres with a crystalline-amorphous interface have been prepared on bimetallic substrate of nickel–iron foam (NIF) by a two-step hydrothermal method. Electrochemical characterization shows that CoWO4/NixFeyS microspheres can boost the electrocatalytic activity effectively through the synergistic effect on the crystalline-amorphous interface. When the CoWO4/NixFeyS is applied as the electrocatalysts for oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER), the overpotentials at a high current density of 500 mA cm−2 are only 322.8 mV and 306.5 mV, respectively. The overall water splitting device composed of CoWO4/NixFeyS/NIF couple only needs a cell voltage of 1.80 V to reach a current density of 100 mA cm−2, and 2.19 V to reach 500 mA cm−2. The CoWO4/NixFeyS/NIF can be also utilized as an effective electrochemical platform for the sensing of toxic hydrazine in a wide range from 50 μM to 17.3 mM, with a detection limit of 46.4 μM. All these results display that the CoWO4/NixFeyS/NIF can be a high-performance multifunctional material for energy transformation and environmental pollutant monitoring.

Hydrothermally Synthesized Z-Scheme Nanocomposite of ZIF-9 Modified MXene for Photocatalytic Degradation of 4-Chlorophenol.

4-Chlorophenol (4CP) is a well-known environmental contaminant often detected in wastewater, generally arising from industrial processes such as chemical manufacture, pharmaceutical production, and pesticide formulation. 4CP is a matter of great concern since it is persistent and has the potential to have harmful impacts on both aquatic ecosystems and human health, owing to its hazardous and mutagenic properties. Hence, degradation of 4CP is of utmost significance. This research investigates the photocatalytic degradation of 4CP using a novel Z-scheme heterojunction nanocomposite composed of MXene and ZIF-9. The nanocomposite is synthesized through a two-step hydrothermal method and thoroughly characterized by using XRD, SEM, UV-visible spectroscopy, zeta potential, and electrochemical impedance spectroscopy studies, confirming successful fabrication with improved surface properties. The comparative photocatalytic degradation studies between pristine materials and the nanocomposite were performed, and significant enhancement in performance was observed. The effect of pH on the degradation efficiency is also explored and correlated with the surface charge. The Z-scheme photocatalysis mechanism is proposed, which is supported by time-resolved photoluminescence studies and scavenger experiments. The reusability of the nanocomposite is also evaluated. The study contributes to the development of efficient and sustainable photocatalysts for wastewater treatment.

Ni3Se4/ZnIn2S4 S-scheme heterojunction for efficient photocatalytic H2 evolution

Photocatalytic water splitting is sustainable technology to obtain green H2. Herein, Ni3Se4/ZnIn2S4 heterojunction was obtained through a two-step hydrothermal method. 5 wt% Ni3Se4/ZnIn2S4 exhibits the most excellent H2 evolution performance and the H2 evolution rate can achieve 38778.0 μmol·g−1·h−1, which is 5.94 times higher than that of pure ZnIn2S4. Based on the ·OH free radical capture tests, the enhanced activity is attributed to S-scheme carriers migration mechanism and the abundant Se sites in Ni3Se4 can rapidly capture H+ to produce H2 efficiently. This work expands the application of transition metal selenides in the field of photocatalysis.

A novel WO3/ZnIn2S4/CoWO4 heterojunction for enhancement of photocatalytic degradation sparfloxacin: Dual S-scheme multi-charge transfer mode and Mechanistic pathway

The novel dual S-scheme WO3/ZnIn2S4/CoWO4 heterojunction was formed by loading WO3 and CoWO4 onto ZnIn2S4 (ZIS) using a simple two-step hydrothermal method. Sparfloxacin (SPX) degradation rate constant of WO3/ZnIn2S4/CoWO4 heterojunction reached 0.0312 min−1, which was nearly 26-, 8.4–34.7-, and 1.6- fold greater than those of WO3, ZIS, CoWO4, and WO3/ZIS, respectively. The multi-charge transfer and separation mechanism of dual S-scheme heterojunction photocatalysts is deeply explored by experiments and density functional theory: the carriers moved in reverse contributed to an interfacial heterotropic built-in electric field, which accelerated the photogenerated carriers’ separation and interfacial transfer ability and lifetime. Further, no recombined electrons and holes with higher reducing and oxidizing properties produced more •O2−, h+ and •OH, which could attack the active atoms of SPX with a high Fukui index. By combining with liquid chromatography mass spectrometry-ion trap-time of flight, plausible SPX degradation intermediates, pathways and mechanisms were presented. SPX was degraded into humic acid-like intermediates, and its environmental risk was significantly reduced. This paper offers insight into developing a novel ZIS-based dual S-scheme heterojunction strategy for solving environmental issues.

Catalytic combustion of 1,2-dichloroethane via C[sbnd]C/C[sbnd]Cl bond cleavage through core-shell structured CeO2@TiO2 catalyst with excellent catalytic performances

A highly representative chlorinated volatile organic compound (Cl-VOCs), including 1,2-dichloroethane (1,2-DCE), which is extremely hazardous to human health and the environment. Improving the catalytic activity is very important for catalytic degradation of 1,2-DCE. In the work, CeO2@TiO2 catalyst which has a core-shell structure were made by a simple two-step hydrothermal synthesis method for 1,2-DCE oxidation. CeO2@TiO2 catalysts show higher activity (T90=275 °C), better carbon dioxide yield (YCO2=89.54 %) and lower by-products production than primitive CeO2 and TiO2. Due to its core-shell structure, CeO2@TiO2 shows the appropriate oxidation and reduction ability and appropriate acidity distribution, the powerful relationship between Ce and Ti elements in CeO2@TiO2 leads to effectively generate activity Ce3+and oxygen, which is greatly great enhance the activity of CeO2@TiO2 in 1,2-DCE catalytic oxidation. Based on the analysis of 1,2-DCE degradation performance and physical and chemical attributes, it proposes a way to catalyze 1,2-DCE catalytic oxidation over CeO2@TiO2. In addition, CeO2@TiO2 has good stability, and adding water vapor over the CeO2@TiO2 during 1,2-DCE degradation to promote 1,2-DCE conversion. The findings of this study might offer some new suggestions for creating catalysts that will destroy Cl-VOCs in their preparation and design.

Synthesis and characterization of Al-doped ZnO/CdO heterostructured nanocomposites for enhancing NO2 gas sensing performance

In this study, both petal-shaped Al-doped (1 at%) ZnO (Al-ZnO) and Al-ZnO/CdO heterostructured nanomaterials were successfully designed and synthesized via a facile two-step hydrothermal method. Characterizations of crystallinity, morphology and composition were performed by XRD, HR-TEM, FE-SEM, EDS, XPS, and Raman. The results of XRD, HR-TEM, and XPS reveal that Al-ZnO/CdO materials grew well together and coexisted. The petal shaped Al-ZnO/CdO heterostructured nanocomposite with 2 mol% of CdO was exposed to NO2, NH3, CH3COCH3, C2H5OH, and H2 at an optimal operating temperature of 200 °C. Compared with pure ZnO and Al-ZnO, the petal-shaped Al-ZnO/CdO heterostructured nanocomposite exhibited specifically high enhanced performances in response and selectivity for the NO2 gas sensing. Moreover, the sensitivity to NO2 displayed excellent linear dependence in the range of 0.5 ∼ 5 ppm, which shows promise in the detection of NO2 using a petal-shaped Al-ZnO/CdO heterostructured nanocomposite-based sensor.

Oxygen-enriched vacancies Co3O4/NiCo2O4 heterojunction hollow nanocages with enhanced electrochemical properties for supercapacitors

Research into environmentally friendly energy storage devices is a vital strategy to address the energy crisis and environmental pollution challenges. In this paper, oxygen-rich vacancy Co3O4/NiCo2O4 heterojunction hollow nanocage electrodes were synthesized by a two-step hydrothermal and calcination method. Taking advantage of its unique structure, oxygen vacancies, and the synergistic effect of multi-element transition metal oxides, the electrode has good conductivity, high specific surface area, and abundant active sites. As a result, the Co3O4/NiCo2O4 HHNCs electrode exhibits an ultra-high specific capacitance of 1788F g−1 at 1Ag-1, and the assembled hybrid supercapacitor has an energy density of up to 43.9 Wh kg−1, which is promising for applications in energy storage materials.

An Ultrasensitive Room-Temperature H2 Sensor Based on a TiO2 Rutile–Anatase Homojunction

Metal oxide semiconductor hetero- and homojunctions are commonly constructed to improve the performance of hydrogen sensors at room temperature. In this study, a simple two-step hydrothermal method was employed to prepare TiO2 films with homojunctions of rutile and anatase phases (denoted as TiO2-R/A). Then, the microstructure of anatase-phase TiO2 was altered by controlling the amount of hydrochloric acid to realize a more favorable porous structure for charge transport and a larger surface area for contact with H2. The sensor used a Pt interdigital electrode. At an optimal HCl dosage (25 mL), anatase-phase TiO2 uniformly covered rutile-phase TiO2 nanorods, resulting in a greater response to H2 at 2500 ppm compared with that of a rutile TiO2 nanorod sensor by a factor of 1153. The response time was 21 s, mainly because the homojunction formed by the TiO2 rutile and anatase phases increased the synergistic effect of the charge transfer and potential barrier between the two phases, resulting in the formation of more superoxide (O2−) free radicals on the surface. Furthermore, the porous structure increased the surface area for H2 adsorption. The TiO2-R/A-based sensor exhibited high selectivity, long-term stability, and a fast response. This study provides new insights into the design of commercially competitive hydrogen sensors.

Controllable Synthesis of Flower-like Hierarchical CuCo2S4 Nanostructure Arrays for High-Performance Hybrid Supercapacitors

Transition metal sulfides (TMSs) are considered as attractive materials in the areas of energy storage because of their unique redox properties, excellent electronic conductivity, as well as environmental friendliness. However, poor cyclic stability and limited electrochemical active sites hinder their further application. To address this issue, a flower-like hierarchical CuCo2S4 structure is constructed by a two-step hydrothermal method. In this nanostructure, CuCo2S4 grows outward to form a tightly bound hierarchical structure on the nickel foams (NFs). This oriented structure can provide more laminar gaps for electrolyte ion diffusion, exposing more reaction sites to increase the ion transport efficiency between the layers, reducing the ion transport resistance and improving the reaction kinetics. Thus, the CuCo2S4 electrode exhibits excellent energy storage performance, exhibiting a high specific capacity of 1415.6 F g−1 at 1 A g−1. After 10,000 cycles of 10 A g−1, it still has 91.9% of the initial performance. In addition, an asymmetrical supercapacitor (ASC) was constructed by choosing CuCo2S4 as the anode and RGO as the cathode, which has the maximum energy density (61.8 Wh Kg−1) at 812.1 W Kg−1 and significant cycling endurance (92.05% retention) at 10,000 turns. Briefly, the researchers successfully constructed an array of CuCo2S4 flower-like hierarchical nanostructures and confirmed their potential application in supercapacitors.