Two-step Hydrothermal Treatment Research Articles

Valorization of residual biomass from the hydrocolloid industry: The role of hydrothermal treatments in the recovery of high-value compounds

Gelidium seaweeds are recognized for their high-quality hydrocolloids, but their industrial extraction leaves behind biomass, whose available valorization approaches are not economically and/or environmentally sustainable. This work aimed to evaluate, for the first time, the effect of batch hydrothermal treatments (and their severity (S0)) on the fractionation of carbohydrates and proteins from this residue. At S0 ≤ 3.13, agars with a maximum gelling strength of 185 g/cm2 can be obtained. At S0 = 3.46, galactose-based non-gelling oligosaccharides are recovered. Harsher processing conditions (S0 ≥ 2.23) result in higher protein solubilization and antioxidant activity. Moreover, sequential processing is a feasible approach to improve process selectivity. A novel proposed two-step hydrothermal treatment (at 200 °C and 230 °C), results in maximum oligosaccharide and protein recovery, leaving behind a cellulose-enriched solid that can be used for biofuel production, in a biorefinery approach.

Facile Synthesis of Ni-Doped WO3-x Nanosheets with Enhanced Visible-Light-Responsive Photocatalytic Performance for Lignin Depolymerization into Value-Added Biochemicals

Lignin is the only renewable resource composed of aromatic hydrocarbons in nature that can be used as raw materials for preparing chemicals. However, due to the existence of stable C–O bonds and C−C bonds in the lignin, the high-value resource utilization of lignin is still challenging work. Herein, we reported efficient lignin depolymerization using a Ni-doped WO3-x nanosheet photocatalyst that was prepared via the two-step hydrothermal treatment. The optimized catalyst (Ni-doped WO3-x) successfully depolymerized sodium lignosulfonate to vanillic acid and guaiacol under visible-light irradiation. The active radicals of photocatalytic depolymerization of sodium lignosulfonate were superoxide radicals, photogenic holes, and hydroxyl radicals under visible-light irradiation. Furthermore, the introduction of Ni significantly decreased the activation energy barrier for selective cleavage of the C−C bond, which was the essential step to promote lactic acid production. This work presented an effective and promising strategy for lignin depolymerization and value-added biochemical production.

Hydrothermal humification of lignocellulosic components: Who is doing what?

The humification behavior of lignocellulosic components (i.e., cellulose, hemicellulose and lignin) under acid-alkali two-step hydrothermal treatment was investigated with particular interest of revealing the contribution of single components as well as their interaction to hydrothermal humic acid (HHA). Lignin with its rich aromatic structures, had the highest HHA contribution (51.8 ± 1.0 wt%), while cellulose and hemicellulose only contributed 8.8 ± 1.6 wt% and 20.1 ± 4.4 wt% HHA yields, respectively. The conversion pathway of these components toward humification indicated that the hydrochar (HC) rather than the hydrothermal solution (HS) had higher humification capability under alkaline hydrothermal conditions because the hydrochar-derived HHA yields of 40.8 ± 2.0 wt% (cellulose), 66.2 ± 6.4 wt% (hemicellulose) and 55.4 ± 6.1 wt% (lignin) were achieved. In addition, co-hydrothermal treatment of cellulose, hemicellulose and lignin under this process improved the HHA production ascribing to the increased HC yield (23.1–53.1 %). The chemical characteristics of HHA products from lignocellulosic components (cellulose, hemicellulose, lignin) and their combinations were similar to the acknowledged natural humic acids. The hydrothermal humification of biowaste mainly passes through a top-down pathway (i.e., HHA forms from the oxidation of large fragments of hydrochar) as well as two bottom-up pathways (i.e., the soluble chemicals conduct the polymerization reaction for HHA production and react with the fragments from HC to synthesize the HHA). This study filled the lack of knowledge in the field of biowaste humification.

Ni3S2 thin-layer nanosheets coupled with Co9S8 nanoparticles anchored on 3D cross-linking composite structure CNT@MXene for high-performance asymmetric supercapacitor

Supercapacitors attract tremendous research attention due to the cost-effectiveness, high power capacity and environment-friendly in the field of energy storage. In this work, Ni3S2 thin-layer nanosheets coupled with Co9S8 nanoparticles anchored on 3D cross-linking composite structure 5 mLCNT@MXene matrix (Ni/Co@C5M) was successfully synthesized via two-step hydrothermal and subsequent annealing treatment, possessing excellent electrochemical performance in terms of high rate capability, superior reversible capacity and outstanding durability. The electrode materials have distinct 3D cross-linking composite structure characteristics, which can significantly boost capacitive storage performance due to the introduction of CNT cross-linking conductive bridges and sulfides. Meanwhile, CNT can also prevent re-stacking of MXene layers and improve the electrical conductivity. As expected, the specific capacitance of Ni/Co@C5M electrode is 1827.5 F g−1 at 1 A g−1, which retains 88.57% after 10,000 cycles at a high current density of 30 A g−1 in cycling stability. Notably, an asymmetric supercapacitor (Ni/Co@C5M as the negative electrode and AC as the positive electrode, Ni/Co@C5M // AC) has exceptionally high energy density up to 78.4 Wh kg−1 at a power density of 699.3 W kg−1 and long capacitance retention of 86.67% at 20 A g−1 for 10,000 cycles. The designed Ni/Co@C5M // AC asymmetric supercapacitor in this work holds a promising future for the upgrading new high-performance energy storage device.

Layered double hydroxide derived cobalt-iron sulfide heterostructures with enhanced reaction kinetics for use in sodium-ion batteries

Constructing a well-designed heterojunction on anodes of sodium ion batteries (SIBs) is an essential strategy for developing high-performance Na-storage devices. In this study, a CoS1.097/FeS lamellar heterostructure was built via a simple two-step hydrothermal treatment using layered double hydroxide precursors. The as-prepared sample exhibits a hydrotalcite-like intercalated structure and heterogeneous composition, which boosts the electrochemical reaction kinetics by shortening the transport distance, unifying move direction and accelerating mobility of Na+. Meanwhile, benefited from such advantages as additional active sites at surfaces, enhanced internal structure stability and relaxed stress from volume expansion etc., SIBs with as-prepared CoS1.097/FeS heterojunction anodes shows excellent sodium storage performances，including high rate capability (564.1 mAh g-1 at 10 A g-1), good the initial coulombic efficiency (80.65% at 0.5 A g-1) as well as great cyclability (543.9 mAh g-1 at 2 A g-1 after 450 cycles). Theoretical calculations based on the first principles are carried out to clarify the possible sodium storage mechanisms. The job may provide a feasible route and key technologies through structural designing and surface coating to prepare anode materials for high-performance sodium-ion batteries. It is expected that the current work can be extended to build other advanced electrode materials for various energy storage related applications.

Effect of magnetite on the catalytic oxidation of polycyclic aromatic hydrocarbons in fly ash from MSW incineration: A comparative study of one-step and two-step hydrothermal processes

Polycyclic aromatic hydrocarbons (PAHs), many of which are carcinogenic, teratogenic, and mutagenic, exist in fly ash (FA) produced from municipal solid waste incineration (MSWI). Hydrothermal treatment (HT) is an efficient approach to remove PAHs from MSWI FA. Here, magnetite (Fe3O4) was used as the catalyst and hydrogen peroxide (H2O2) as the oxidant for one-step and two-step catalytic hydrothermal methods. When the magnetite dosage increased to 15 wt%, the maximum degradation rates of PAHs were 84.36% and 92.51%, respectively; however, the toxicity equivalent quantity (TEQ) degradation rates of the PAHs both increased upon increasing the magnetite dose. At 20 wt% Fe3O4, the maximum TEQ degradation rates of the PAHs were 93.29% and 97.76%, respectively. The reaction between OH and PAHs is non-selective, which means that LMW, MMW, and HMW PAHs were all degraded. The decrease in TEQ was mainly due to the degradation of HMW PAHs, i.e., those with five rings. Under the same Fe3O4 dose, oxidant dose, and reaction time, the detoxification of PAHs by the two-step method was significantly better than that of the one-step method, possibly because the two-step method more effectively produced OH. The first step degraded more than 90% of PAHs, and the residual PAHs in the HT products of the first step limited the utilization of the oxidant during the second step. The minerals in the HT products implied that the two-step hydrothermal method not only produced more OH, which reacted with PAHs, but also generated metal-magnetite substitution, which affected its surface reactivity during heavy metal adsorption and catalysis. These results revealed that both magnetite and the two-step hydrothermal treatment degraded PAHs. 20 wt% magnetite was the optimal amount during the two-step hydrothermal catalytic oxidation of MSWI FA.

Fast and Durable Potassium Storage Enabled by Constructing Stress-Dispersed Co3Se4 Nanocrystallites Anchored on Graphene Sheets.

Transition metal dichalcogenides are regarded as promising anode materials for potassium-ion batteries (PIBs) because of their high theoretical capacities. However, due to the large atomic radius of K+, the structural damage caused by the huge volume expansion upon potassiation is much more severe than that of their lithium counterparts. In this research, a stress-dispersed structure with Co3Se4 nanocrystallites orderly anchored on graphene sheets is achieved through a two-step hydrothermal treatment to alleviate the structural deterioration. The ability to reduce the contact stress by the well-dispersed Co3Se4 nanocrystallites during K+ intercalation, together with the highly conductive graphene matrix, provides a more reliable and efficient anode architecture than its two agminated counterparts. Given these advantages, the optimized electrode delivers excellent cycling stability (301.8 mA h g-1 after 500 cycles at 1 A g-1), as well as an outstanding rate capacity (203.8 mA h g-1 at 5 A g-1). Further in situ and ex situ characterizations and density functional theory calculations elucidate the potassium storage mechanism of Co3Se4 during the conversion reaction and reveal the fast electrochemical kinetics of the rationally designed electrode. This work provides a practical approach for constructing stable metal-selenide anodes with long cycle life and high-rate performance for PIBs.

Double ion-exchange reaction-based photoelectrochemical immunoassay for sensitive detection of prostate-specific antigen

This work developed a double ion-exchange reaction-based photoelectrochemical (PEC) immunoassay with the split-type detection mode for sensitive detection of prostate-specific antigen (PSA, used as a model). The nanocomposite of cadmium sulfide and nickel sulfide (CdS@NiS nanocomposite), as the photoactive material, was rapidly synthesized by two-step hydrothermal treatment. In the presence of target PSA, the cupric oxide nanoparticle (CuO NP) labeled detection antibody was introduced into the detection system by sandwich immunoreaction and the copper (Cu2+) ions was released from CuO nanoparticles by acid to participate in double ion-exchange reaction. The double ion-exchange reaction on the photoelectric sensing interface between Cu2+ and CdS@NiS nanocomposites formed the weak photoactive material CuxS (x = 1, 2) to reduce the photocurrent. Under optimal conditions, the double ion-exchange reaction-based PEC immunoassay exhibited good photocurrent responses toward target PSA within the dynamic working range from 0.01 ng mL−1 to 50 ng mL−1 at a low limit of detection (LOD) of 2.9 pg mL−1. Besides, our work could achieve good reproducibility and high specificity under the split-type detection mode. Compared with human PSA ELISA kit, the accuracy obtained by our strategy was satisfactory. Importantly, this Cu2+-activated double ion-exchange reaction-based PEC immunoassay provides a promising platform for the detection of biomarkers.

A Promising Electrochemical Platform for Dopamine and Uric Acid Detection Based on a Polyaniline/Iron Oxide-Tin Oxide/Reduced Graphene Oxide Ternary Composite.

A ternary polyaniline/Fe2O3-SnO2/reduced graphene oxide (PFSG) nanocomposite was prepared using a simple two-step hydrothermal treatment. The composite was applied as a glassy carbon electrode modifier (GCE) to enhance dopamine (DA) and uric acid (UA) detection. The ternary PFSG composite was compared with its binary precursor Fe2O3-SnO2/reduced graphene oxide (FSG). The influence of the modified GCE electrodes on their performance as a sensing platform was determined. GCE/PFSG showed better sensing parameters than GCE/FSG due to the introduction of polyaniline (PANI), increasing the electrocatalytic properties of the electrode towards the detected analytes. GCE/PFSG enabled the detection of low concentrations of DA (0.076 µM) and UA (1.6 µM). The peak potential separation between DA and UA was very good (180 mV). Moreover, the DA oxidation peak was unaffected even if the concentration of UA was ten times higher. The fabricated sensor showed excellent performance in the simultaneous detection with DA and UA limits of detection: LODDA = 0.15 µM and LODUA = 6.4 µM, and outstanding long-term stability towards DA and UA, holding 100% and 90% of their initial signals respectively, after one month of use.

Nano tree-like branched structure with α-Ga2O3 covered by γ-Al2O3 for highly efficient detection of solar-blind ultraviolet light using self-powered photoelectrochemical method

For photoelectrochemical ultraviolet detector, carrier recombination, low light trapping efficiency and long-distance charge carries transport are the main factors restricting its detection performance. Herein, a novel tree-like branched structure with α-Ga2O3 covered by γ-Al2O3 has been successfully fabricated by simple two-step hydrothermal treatment and applied into the self-powered photoelectrochemical solar-blind detector. Owning to the introduction of γ-Al2O3 layer with ultra-wide bandgap to coat outside of α-Ga2O3, an energy barrier has been established at the semiconductor/electrolyte interface accelerating the photogenerated carriers separation and thus suppressing interfacial charge recombination. Besides, the obtained tree-like branched structure significantly expands the contact surface area between carries and electrolyte to shorten the distance of charge transport improving response speed and brings a larger specific surface area to capture and scatter incident photons enhancing light absorption. Campared with the pure α-Ga2O3, the α-Ga2O3-γ-Al2O3 based on the photoelectrochemical device shows higher responsivity, larger photocurrent density and faster response time to solar-blind ultraviolet signal, some performance improvements exceed 100%, indicating the highly efficient detection.

Designed fabrication of sulfide-rich bi-metallic-assembled MXene layered sheets with dramatically enhanced photocatalytic performance for Rhodamine B removal

Herein, a two-step hydrothermal treatment was used to synthesize a novel hybrid photocatalyst with sulfide-rich layered double hydroxides intercalated MXene for the degradation of rhodamine B (RhB). The fabricated NiCo2S4 on MXene (denoted as NCS@MX) photocatalyst showed higher catalytic activity and degraded RhB to approximately ≈100% within 20 min under visible light irradiation. The optical response and recombination rate used increased the separation efficiency of photoinduced e− and h+ by NCS@MX, thus enhancing the photocatalytic degradation of RhB. The OH and O2− radicals were non-toxic by-products of the NCS@MX system for the mineralization of organic pollutants. Furthermore, NCS@MX exhibited great photo-stability in five repetitive runs for the degradation of RhB with a minimal drop on catalytic activity. Possible oxidative pathways of RhB and the reaction intermediates were observed by liquid chromatography-mass spectrometry (LC-MS). The pollutant was primarily oxidized into non-toxic products such as H2O, CO2, and few inorganic species. Therefore, NCS@MX is expected to have prospects for applications in wastewater management considering its environmental friendliness, low-cost, and non-toxic by-products production.

Facile synthesis of nanoflower-like phosphorus-doped Ni3S2/CoFe2O4 arrays on nickel foam as a superior electrocatalyst for efficient oxygen evolution reaction

Developing cost-effectiveness and superior electrocatalysts is crucial to improve the efficiency of oxygen evolution reaction (OER) in water splitting system. Hence, flower-like phosphorus doped Ni3S2/CoFe2O4 arrays (P-Ni3S2/CoFe2O4/NF) were generated on three-dimensional (3D) nickel foam (NF) via the two-step hydrothermal treatment and subsequent phosphorization. Additionally, a series of control experiments were conducted to investigate the formation mechanism. By virtue of the unique 3D configurations and multi-compositions, the as-prepared catalyst exhibited greatly improved OER performance in 1.0 M KOH solution, with the overpotential of only 254 mV at 50 mA cm−2 and low Tafel slope of 54.43 mV dec−1. This study provides a feasible approach for preparing advanced electrocatalyst in energy conversion and storage devices.

Two-step hydrothermal synthetic method of niobium-tungsten complex oxide and its adsorption of methylene blue

Niobium-tungsten oxide Nb18W16O9 was successfully synthesized by a two-step hydrothermal process and heat treatment. The structural and characteristics of samples and their adsorption of methylene blue (MB) have been investigated by XRD, SEM and UV–Vis spectrometer. Structural results indicated that the sample obtained through heat-treatment in the case of pH = 3 is a niobium-tungsten oxide (Nb18W16O93) with Pbam space group. Meanwhile, adsorption of methylene blue on niobium-tungsten complex oxide showed that the calcined sample with nanobar-shape synthesized by a two-step hydrothermal process in pH range of 3 adsorbed above 97% methylene blue with the concentration of 10 mg/L in 5 min at room temperature. Also, it has been showed that its adsorption is superior to an as-hydrothermal prepared sample.

Synthesis of Metal Phosphide Nanoparticles Supported on Porous N‐Doped Carbon Derived from Spirulina for Universal‐pH Hydrogen Evolution

Transition metal phosphides (TMPs) are regarded as highly active electrocatalysts for the hydrogen evolution reaction (HER). However, traditional synthetic routes usually use expensive and dangerous precursors as P donors. The development of a low-cost and ecofriendly method for the synthesis of TMPs is significant for sustainable energy development. Herein, cobalt phosphides anchored on or embedded in a spirulina-derived porous N-doped carbon matrix (Co2 P/NC) was fabricated by two-step hydrothermal treatment and carbonization method, which utilized the intrinsic C, N, and P of biomass cleverly as the sources of C, N, and P, respectively. As a result of the high surface area and porosity that enhance the mass-transfer dynamics, Co2 P/NC shows good electrocatalytic activity at all pH values in the HER. This work not only provides a facile and effective method for the fabrication of TMP nanoparticles loaded onto carbon materials but also opens a new strategy for the utilization of the intrinsic ingredients of biomass for the preparation of other functional electrocatalysts.

Hierarchical ZSM-5 based on fly ash for the low-temperature purification of odorous volatile organic compound in cooking fumes

Hierarchical ZSM-5 (HZ) zeolites with different SiO2/Al2O3 ratios (SiO2/Al2O3 = 50, 100, 150, 200, 250 and 300) were synthesized using a two-step hydrothermal treatment method, and the Al and Si were obtained from fly ash by the alkali melting and acid leaching method. On this basis, the 10 wt% LaMnO3/HZ catalysts were prepared by impregnation. The all the synthesized catalysts were investigated for the low-temperature (200 °C) catalytic oxidation of pentanal, which was selected as a typical odorous volatile organic compound (VOC) in cooking fumes. In addition, the physicochemical properties of HZ zeolites were characterized by several techniques (XRD, N2 physical adsorption–desorption, ICP-OES, SEM,TEM,NH3-TPD and 27Al MAS-NMR). The results showed that the HZ zeolite, which was micro-mesoporous material and had high specific surface area, provided a higher diffuser efficiency for long-chain VOC gas. The catalytic performance of HZ zeolite was better than that of the traditional ZSM-5 zeolite. Compared with the dry atmosphere, HZ-100 zeolite, which possessed more proper medium strong acid sites and the appropriate amount of acid sites, had the higher pentanal catalytic combustion conversion of above 92% and the relatively superior stability with 2 V% water steam in air, indicating that the suitable acid sites can form the best synergistic catalytic effect with water molecules for purifying long-chainVOC gas. In addition, the catalytic conversion of pentanal on 10 wt% LaMnO3/HZ-100 was 100% with no deactivation, and compared with HZ under a dry atmosphere, the average CO2 yields of 10 wt% LaMnO3/HZ catalysts in the steady catalytic oxidation stage under a dry atmosphere and 2 V% water steam in air were improved by 6–18% and 13–20%.

Fabrication of uniform urchin-like N-doped NiCo2O4@C hollow nanostructures for high performance supercapacitors.

Transition metal oxides are commonly used in electrochemical energy storage materials, but there are still many drawbacks that impede a wide range of applications. Heteroatom doping can significantly improve its performance. Herein, we have successfully prepared highly uniform N-doped NiCo2O4@C hollow nanostructures for supercapacitors by a two-step hydrothermal treatment associated with successive annealing process. Prepared N-doped NiCo2O4@C materials exhibited an admirable specific capacitance of 1028 F g−1 at a current density of 3 A g−1, with 625 F g−1 remaining even at high current density of 20 A g−1. Besides, this composite showed good electrochemical stability with capacity retention of 84% after 5000 cycles repetitive galvanostatic charge–discharge test at 10 A g−1. An asymmetric supercapacitor was assembled by the N-doped NiCo2O4@C electrode, attached activate carbon (AC) as a counter electrode, exhibiting a high energy density of 26.67 W h kg−1 at a power density of 402 W kg−1. The improvement of electrochemical performance is ascribed to the co-doping of nitrogen and carbon atoms. These results indicate that N-doped NiCo2O4@C can be employed as an ideal electrode material for electrochemical energy storage.

Synergistic adsorption of Cu(II) and photocatalytic degradation of phenanthrene by a jaboticaba-like TiO2/titanate nanotube composite: An experimental and theoretical study

Combined water pollution with the coexistence of heavy metals and organic contaminants is of great concern for practical wastewater treatment. In this study, a jaboticaba-like nanocomposite, titanate nanotubes supported TiO2 (TiO2/TiNTs), was synthesized by a two-step hydrothermal treatment. TiO2/TiNTs had large surface area, abundant of –ONa/H groups and fine crystal anatase phase, thus exhibited both good adsorptive performance for Cu(II) and high photocatalytic activity for phenanthrene degradation. The maximum Cu(II) adsorption capacity on TiO2/TiNTs was 115.0 mg/g at pH 5 according to Langmuir isotherm model, and >95% of phenanthrene was degraded within 4 h under UV light. TiO2/TiNTs showed about 10 times higher observed rate constant (kobs) for phenanthrene degradation compared to the unmodified TiNTs. More importantly, the coexistence of Cu(II) promoted photocatalytic degradation of phenanthrene, because the incorporated Cu(II) in the lattice of TiNTs could trap photo-excited electron and thus inhibited the electron-hole recombination. Density functional theory (DFT) calculation indicated that the sites of phenanthrene with high Fukui index (f0) preferred to be attacked by OH radicals. The quantitative structure–activity relationship (QSAR) analysis revealed that the degradation intermediates had lower acute toxicity and mutagenicity than phenanthrene. TiO2/TiNTs also owned high stability, as only slight loss of Cu(II) and phenanthrene removal efficiency was observed even after four reuse cycles. The developed material in this study is of great application potential for water or wastewater treatment with multi-contaminants, and this work can help us to better understand the mechanisms on reaction between Ti-based nanomaterials and different kinds of contaminants.

Spatially-controlled NiCo2O4@MnO2 core–shell nanoarray with hollow NiCo2O4 cores and MnO2 flake shells: an efficient catalyst for oxygen evolution reaction

Control of structures and components of the nanoarray catalysts is very important for electrochemical energy conversion. Herein, unique NiCo2O4@MnO2 core–shell nanoarray with hollow NiCo2O4 Cores and MnO2 flake shells is in situ fabricated on carbon textile via a two-step hydrothermal treatment followed by a subsequent annealing. The as-made nanoarray is highly active and durable catalyst for oxygen evolution reaction in alkaline media attribute to the synergetic effect derived from spatially separated nanoarray with favorable NiCo2O4 and MnO2 compositions.

Large-Area Schottky Junctions between ZnO and Carbon Nanotube Fibres.

In this study, large-area (10 cm2 ) samples of heterojunctions between zinc oxide and carbon nanotube (CNT) fibre arrays were synthesised. A two-step hydrothermal treatment was used to grow Zn nanowires (NWs) in situ directly onto the CNT array. This resulted in a bulk heterojunction that consisted of a five-micron layer of ZnO crystals in contact with the built-in CNT fabric current collector, with preferential orientation of the ZnO c axis perpendicular to the CNT sheet. The electrical properties of the heterojunction corresponded to a Schottky junction with a barrier height of 0.26 eV and an ideality factor of 2.9. Photoconductivity measurements indicated charge transfer through the ZnO/CNT interface, thus leading to a gain factor of approximately 100 and a responsivity as high as 5000 mA w-1 under UV irradiation. The resulting ZnO/CNT fibre hybrid was both piezoresistive and piezoelectric under transverse compression with an attractive format for energy-harvesting applications.

A bifunctional NiCo2S4/reduced graphene oxide@polyaniline nanocomposite as a highly-efficient electrode for glucose and rutin detection

A novel NiCo2S4/reduced graphene oxide@polyaniline (NiCo2S4/rGO@PANI) composite was synthesized by a facile two-step hydrothermal treatment and calcination, which was coupled with an in situ polymerization process.