Effect Of Hydrothermal Temperature Research Articles

The Effects of Hydrothermal Temperatures on ZnO-Bentonite Composite Synthesis on Adsorption and Photodegradation of Methylene Blue Dye

This study explores the influence of hydrothermal temperatures on the synthesis of ZnO-Bentonite composites and their efficiency in the adsorption and photodegradation of Methylene Blue dye. ZnO nanoparticles were integrated into Na-Bentonite, with composites synthesized at hydrothermal temperatures of 100°C and 200°C. Various characterization techniques such as XRD, FTIR, UV-Vis DRS, TG-DTA and BET were utilized to analyze the structural and thermal properties. The results show that the composite synthesized at 200°C exhibits superior performance, with a maximum adsorption capacity of 120.48 mg/g at 50°C, significantly higher than the 49.26 mg/g achieved by the composite synthesized at 100°C. Moreover, the enhanced crystallinity and increased surface area, as evidenced by a 16 nm crystallite size at 100°C and 22 nm at 200°C, led to improved photocatalytic activity. The research concludes that higher hydrothermal temperatures improve both adsorption and photodegradation efficiency, making the composite synthesized at 200°C more effective for environmental applications.

Effect of hydrothermal temperature on the optical properties of hydrochar-derived dissolved organic matter and their interactions with copper (II)

Hydrothermal carbonization (HTC) has been regarded as a promising technique for turning wet biomass into hydrochar due to its low energy consumption, low exhaust gas emissions, etc. In addition, hydrochar is an important source of dissolved organic matter (DOM), which plays a crucial part in the migration and destiny of pollutants in the environmental medium. However, there are limited studies that focus on the factors that influence the formation of DOM in hydrochar, such as hydrothermal temperature. Therefore, the current study comprehensively characterized the optical properties of DOM within hydrochar derived from sawdust (HDOM) under different hydrothermal temperatures (150–300 °C) by Ultraviolet–visible (UV–Vis) and fluorescence spectroscopy, as well as its complexation characteristic with Cu(II). The findings revealed that the organic carbon content of HDOM reached a peak of 37.3 mg L−1 when the temperature rose to 240 °C and then decreased as the temperature increased. UV–Vis spectroscopy analysis showed that the absorption capacity of HDOM at 275 nm increases with temperature and reaches a maximum value at 240 °C, indicating that high temperature promotes the formation of monocyclic aromatic compounds. High temperature enhances the aromaticity, hydrophobicity, and humification degree of HDOM, thus improving its stability and aromaticity. The E3/E4 ratios are all greater than 3.5, confirming that the main component of HDOM is fulvic acid, which corresponds to 3D-EEM and Pearson's correlation coefficient analysis. The humification index (HIX) of HDOM increased with the rise in hydrothermal temperature (150–240 °C), as observed by the three-dimensional excitation-emission matrix spectroscopy (3D-EEMs). After reaching its peak at 240 °C, the HIX value gradually dropped in line with the trend of the DOC change. Moreover, the bioavailability (BIX) value of DOM was all high and greater than 1, indicating all the HDOM are readily bioavailable. Two microbial humic substances (C1 and C4), a humic-like substance (C2), and a protein-like substance (C3) were discovered in DOM by integrating 3D-EEMs with parallel factor analysis (PARAFAC). Their fluorescence intensity decreases as the Cu(II) concentration increases, indicating the formation of complexes with Cu(II). As the temperature rises, the binding ability of DOM and Cu(II) changes significantly, reaching the optimum at 300 °C. Meanwhile, the substance C2 has the strongest binding ability with Cu(II). This research emphasizes the significance of spectroscopy analysis in determining the evolution of hydrochar-derived DOM, the potential for heavy metal binding and migration, and its characteristics and features.Graphical

Effect of hydrothermal temperature on the structural, morphological, optical properties and photocatalytic performances of cobalt sulfide nanomaterials

The powders of cobalt sulfide were successfully synthesized using hydrothermal technique at various temperatures (180, 200 and 220 °C). X-ray diffraction revealed that the resulting samples are the hexagonal CoS, and the cubic Co9S8. Fourier transform infrared further verified the cobalt sulfide formation, showing Co-S band vibrations at 600 cm-1 across all samples. Scanning electron microscopy unveiled diverse hierarchical morphologies with notable porosity. Energy-dispersive X-ray microanalysis revealed the purity of samples, showing no traces of impurities. Electrochemical impedance spectroscopy showed a charge transfer phenomenon in the high-frequency range. The optical band gap energies (Eg) were determined using the Tauc model, yielding 1.95 eV for CoS and 2.81 eV for Co9S8. The photocatalytic efficiency of cobalt sulfides for dye degradation was assessed employing methylene blue as a model colorant through photocatalytic technology. This study underscores all samples as efficient and stable photocatalysts, especially the CoS-Co9S8 mixture phases.

Effects of production temperature on the molecular composition and seed-germination-promoting properties of sludge-based hydrochar-derived dissolved organic matter

Sludge hydrothermal carbonization demonstrates potential for converting sludge into multifunctional carbon materials for soil remediation. However, the influence of dissolved organic matter (DOM) with unclear molecular characteristics in sludge-based hydrothermal carbon on plant growth has not been sufficiently investigated. Herein, the effects of hydrothermal temperature on the molecular transformation pathways and plant-growth-promoting properties of DOM were investigated via FT-ICR MS–based molecular network analyses and seed germination experiments. Results indicated that the highest DOM yield was achieved at 220 °C. During low-temperature (180 °C) hydrothermal treatment, the hydrolysis of biopolymers, as well as the partial condensation and cyclization of small-molecule intermediates, occurred in the sludge. This process produced unsaturated CHNO compounds containing one or two N atoms, which promoted seed germination. Further, the toxicity of DOM to plants increased with rising hydrothermal temperature. This was accompanied by S doping and aromatization reactions, which mitigated the effects of plant growth hormones. This study provides theoretical support for the optimization of sludge hydrothermal treatment and production of plant growth hormones, enhancing the ecological value of sludge-based hydrochar.

Enhanced Piezo‐photocatalytic Performances of AgNbO3 Materials for Dye Decomposition Via Polarization Engineering

AbstractThe limitation to enhancing photocatalytic performance in photocatalysts lies in the rapid recombination of photo‐induced electrons and holes. Herein, AgNbO3 photocatalysts were synthesized by the hydrothermal method. The effects of hydrothermal temperature on the microstructure and photocatalytic/piezo‐photocatalytic performances of AgNbO3 have been systematically investigated. The AgNbO3 cubes synthesized at 180 °C for 24 h exhibited the best photocatalytic/piezo‐photocatalytic performances among all samples. The corona poling as an important method of polarization engineering is applied to promote further the separation and migration of charge carriers in AgNbO3. The polarized AgNbO3 synthesized at 170 °C exhibited outstanding piezo‐photocatalytic performance, and a degradation rate of 95 % for RhB within 90 min and a high apparent rate constant of 0.02978 min−1 were achieved. On the one hand, the alternating piezoelectric field caused by ultrasonic‐assisted illumination destroyed the shielding effect and enhanced the separation of electron‐hole pairs. On the other hand, polarization engineering induced by corona poling promoted the separation and migration of photo‐induced carriers, thereby realizing more efficient utilization of these charges during the photocatalytic decomposition process. This work presents a facile way to achieve superior piezo‐photocatalytic performances of AgNbO3‐based photocatalyst via polarization engineering.

Reduction of graphene oxide (GO) to reduced graphene oxide (rGO) at different hydrothermal temperatures and enhanced photodegradation of zinc oxide/rGO composites

Scholars are shifting their attention to the development of environmentally friendly materials with a high degradability of environmental pollutants. Among various photocatalytic materials, zinc oxide (ZnO)/reduced graphene oxide (rGO) nanomaterials can meet these requirements. In this study, ZnO/rGO nanomaterials with different hydrothermal temperatures were fabricated through a hydrothermal method. We determined the hydrothermal temperature variations to create different structures and identify the morphologies and sizes of the ZnO/rGO material. The average crystal size of ZnO/rGO nanomaterials decreased from 32.25 nm to 30.30 nm when the hydrothermal temperature was increased from 100 °C to 180 °C. The detailed x-ray diffraction (XRD) study showed that the diffraction peak position of ZnO decreased, the lattice constant increased, and the unit cell volume increased with the increase in hydrothermal temperature. rGO-related diffraction peaks were also observed in the XRD patterns of ZnO/rGO samples, which indicates the formation of a ZnO/rGO crystalline structure. Fourier transform infrared spectra revealed the chemical bonding of ZnO and rGO materials. The photoluminescence (PL) spectra of ZnO/rGO nanocomposites presented two characteristic emission peaks at 383 and 558 nm. The Raman scattering spectra of ZnO/rGO nanomaterials exhibited ZnO-related peaks at 329, 436, and 1123 cm−1 and rGO-related peaks at 1352, 1579, 2706, and 2936 cm−1. The ultraviolet-visible (Vis) absorption spectra of ZnO/rGO nanomaterials manifested the characteristic absorption peaks of ZnO and rGO at 381 and 291 nm, respectively. The photocatalytic properties of ZnO/rGO nanomaterials were studied through the decomposition of methylene blue (MB) under Vis light. The effect of hydrothermal temperature on the properties of ZnO/rGO materials and the photodecomposition mechanism of MB were investigated in detail.

Photocatalytic Gold Recovery from Industrial Gold Plating Effluent by ZnO Nanoparticles: Optimum Condition and Possible Applications.

The comparative study of photocatalytic gold recovery from cyanide-based gold plating solution was explored via commercial and hydrothermally synthesized ZnO nanoparticles (NPs). The effects of hydrothermal temperatures on the properties and photocatalytic activities of synthesized ZnO NPs were investigated. In addition, the effects of operating parameters including types of hole scavenger, concentrations of the best hole scavenger, the initial pH of wastewater, and photocatalyst dosages were examined. The obtained results demonstrated that the commercial ZnO NPs exhibited a higher photocatalytic activity for gold recovery than that of the synthesized ones owing to their good crystal quality and the presence of non-lattice zinc ions and appropriate non-lattice oxygen ions. Via the commercial ZnO NPs, the gold ions were almost completely recovered from the cyanide-based gold plating effluent within 7 h at an initial pH of 11.0 in the presence of 10 vol % C2H5OH and 1.0 g/L of photocatalyst loading with a pseudo-first-order rate constant of 0.2637 h-1. Finally, the resultant gold-decorated ZnO NPs exhibited a higher photocatalytic property for color reduction from industrial wastewater and antibacterial activity than that of fresh ZnO NPs. The results obtained in this study possess benefits and pave the way for waste remediation and management for the plating industries.

Construction of Co/Mn-based nanowires with adjustable surface state for boosting lean methane catalytic oxidation

In this paper, CoMn based nanowires were in-situ grown on foam nickel by hydrothermal method combined with calcination treatment, and a monolithic methane oxidation catalyst was obtained. The effects of hydrothermal temperature and calcination temperature on the crystal structure, micro morphology and catalytic performance of the catalysts were systematically studied. The results indicated that when the hydrothermal temperature was 160 °C and the calcination temperature was 350 °C, Mn doped Co3O4 nanowires with uniform morphology can be obtained, accompanied by the appearance of CoMn2O4. The introduction of Mn ions caused lattice distortion of Co3O4, achieving the regulation of adsorbed oxygen and lattice oxygen. The monolithic MnCoO/NF–H-160 °C catalyst showed the best catalytic activity (T90 = 414 °C) for lean methane catalytic oxidation, which even surpassed the noble metal based catalyst. Its excellent catalytic activity was due to the fact that the catalyst can expose more active sites, rich active oxygen and good mass transfer characteristics. This study provides a new approach for designing efficient monolithic catalysts and has significant potential for application and development in the field of organic waste gas treatment.

Nanoarchitectonics of nest-like Co3O4 nanowires embedded nitrogen-doped graphene aerogel as electrochemical sensing platform for Pb2+ and Cd2+ trace detection

Nano Co3O4 embedded nitrogen-doped graphene aerogel (Co3O4@NGA) was directly prepared by one-pot hydrothermal synthesis method with ammonia water acting as both precipitant of Co3O4 and nitrogen source of nitrogen-doped graphene aerogel (NGA). This novel method leaved out the calcination process which was necessary for most methods to prepare Co3O4 nanomaterials. The effects of hydrothermal temperature on both morphologies and Pb2+/Cd2+ electrochemical detection performances of Co3O4@NGA were explored. As the hydrothermal temperature rising from 140 °C to 200 °C, the shapes of Co3O4 changed from nanoparticles to nanowires and then to nanoflowers, and nest-like Co3O4 nanowires were architected on NGA sheets at 180 °C. The electrochemical sensor based on the optimized Co3O4@NGA-180 exhibited low limit of detection (LOD) for Pb2+ (7.2 nM) and Cd2+ (10.06 nM) and high sensitivity for Pb2+ (10.51 μA·μM−1) and Cd2+ (8.053 μA·μM−1). The excellent performances were attributed to the synergistic effect of Co3O4 nanowires and porous NGA, which leaded to the fast electrochemical reaction rate in the detection process. Moreover, the Co3O4@NGA-180/GCE sensor had excellent selectivity, repeatability and stability, and could be used to detect traces of Pb2+ and Cd2+ in real water sample.

Investigating the Supercapacitive Performance of Cobalt Sulfide Nanostructures Prepared Using a Hydrothermal Method

In this study, we synthesized cobalt sulfide (CoS) nanostructures for supercapacitor applications via a one-step hydrothermal method. The effect of hydrothermal temperature on the synthesis process was investigated at temperatures ranging from 160 °C to 220 °C. The structural, morphological, and elemental analyses were performed using X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), and scanning electron microscopy (SEM). The XRD patterns show the hexagonal phase of CoS, and the samples prepared at 200 °C have high crystallinity. The samples prepared at other temperatures show amorphousness at lower 2-theta angles. EDX indicated that the sample was of high purity, except that the sample prepared at 220 °C had an additional oxygen peak, indicating that sulfur is not stable at high temperatures. In addition, a cobalt oxide (CoO) peak is also observed in the XRD data of the sample prepared at 220 °C. SEM images show that the particles in the samples prepared at 160 °C and 180 °C are agglomerated due to the high surface energy, whereas the samples prepared at 200 °C and 220 °C have a distinct morphology. Electrochemical analyses such as cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge–discharge (GCD) were performed on all samples. The CoS sample prepared at 200 °C exhibited a high specific capacitance (Csp) of 1583 F/g at a current density of 1 A/g, with low resistivity and high cycling stability.

Facile synthesis of β-MnO2 via ozone oxidation for enhanced performance of toluene oxidation

In this work, a series of β-MnO2 catalysts is directly synthesized via ozone oxidation using the hydrothermal method. And the effect of hydrothermal temperature on catalytic activities of toluene oxidation is investigated. The catalytic evaluation shows that O3(HT)-160 prepared at 160 °C of hydrothermal temperature exhibits the best catalytic activity of toluene oxidation compared with other catalysts. By comparison of physicochemical properties, O3(HT)-160 possesses a bigger specific surface area and larger pore volume, which are beneficial to the adsorption and diffusion of toluene molecules. Meanwhile, O3(HT)-160 performs lower reductive temperature, higher ratio of Mn4+/(Mn3++ Mn2+) and Olatt/Oads and much more oxygen vacancies, which contributes to the cycle of redox ability, the complete oxidation of intermediates and the activation of oxygen. Moreover, combined with the results of in-situ DRIFTS and TD/GC–MS, the main intermediates are benzyl alcohol, benzaldehyde, benzoic acid and propylene glycol during toluene oxidation on O3(HT)-160. Furthermore, the catalytic mechanism is proposed for toluene oxidation on O3(HT)-160. This work provides a more convenient and simpler method to prepare β-MnO2 using ozone as the oxidizer compared with potassium permanganate and potassium persulfate.

Release characteristics of hydrochar-derived dissolved organic matter: Effects of hydrothermal temperature and environmental conditions

Much research has been done on the preparation and application of hydrochars, but research on the release characteristics of hydrochar-derived dissolved organic matter (HDOM) is very limited; clarifying the release characteristics of HDOM is important for understanding and adjusting the environmental behaviour of hydrochar. Herein, the potential release of HDOM from rice straw-derived hydrochars prepared at different hydrothermal temperatures was investigated under various potential environmental conditions for the first time. The total release quantity and humification degree of HDOM decreased with increasing hydrothermal temperature. The critical dividing line for various hydrothermal reactions, decomposition and polymerization, was in the range of 240 °C–260 °C. Alkaline condition increased the HDOM release amount (up to 299 mg g−1), molecular weight (as high as 423 Da) and molecular diversity (8857 compounds) from rice straw-derived hydrochars. The unique substances of HDOM released under alkaline condition were mainly distributed in lipids-like substances, CRAM/lignins-like substances, aromatic structures, and tannins-like substances, while few unique substances were found under acidic condition. Additionally, CRAM/lignins-like substances were the most abundant in all HDOM samples, reaching 82%, which were relatively stable and could achieve carbon sequestration in different environments. The findings provided a new insight on understanding the potential environment behaviors of hydrochar.

A heterogeneous double chamber electro-Fenton with high production of H2O2 using La–CeO2 modified graphite felt as cathode

Hydrogen peroxide synthesis by electro-reduction of O 2 to substitute the current anthraquinone process has attracted a great deal of attention. Low oxygen utilization rate and low hydrogen peroxide production remain obstacles to electro-Fenton application. In situ H 2 O 2 generated by electrochemical reaction depends on the electrochemical performance of the cathode and the structure of the reactor. Here, novel graphite felt (GF) modified by La-doped CeO 2 (La–CeO 2 ) was developed as a cathode. A new double chamber electro-Fenton reactor was proposed, where an organic ultrafiltration membrane was used to prevent H 2 O 2 from spreading to the anode. The effects of hydrothermal temperature, time and urea concentration on the electrochemical properties of graphite felt were investigated. The accumulated concentration of H 2 O 2 on the modified cathode reached 218.4 mg·L –1 in 1 h when the optimal conditions of hydrothermal temperature 120 °C and urea concentration 0.55% (mass) in 24 h. The degradation rate of methyl orange reached 98.29%. The new electro-Fenton reactor can efficiently produce hydrogen peroxide to degrade various organic substances and has a high potential for treating wastewater in the chemical industry.

Morphological Control of Supported ZnO Nanosheet Arrays and Their Application in Photodegradation of Organic Pollutants.

Supported nanostructured photocatalysis is considered to be a sustainable and promising method for water pollution photodegradation applications due to its fascinating features, including a high surface area, stability against aggregation, and easy handling and recovery. However, the preparation and morphological control of the supported nanostructured photocatalyst remains a challenge. Herein, a one-step hydrothermal method is proposed to fabricate the supported vertically aligned ZnO nanosheet arrays based on aluminum foil. The morphologically controlled growth of the supported ZnO nanosheet arrays on a large scale was achieved, and the effects of hydrothermal temperature on morphologic, structural, optical, and photocatalytic properties were observed. The results reveal that the surface area and thickness of the nanosheet increase simultaneously with the increase in the hydrothermal temperature. The increase in the surface area enhances the photocatalytic activity by providing more active sites, while the increase in the thickness reduces the charge transfer and thus decreases the photocatalytic activity. The influence competition between the area increasing and thickness increasing of the ZnO nanosheet results in the nonlinear dependence between photocatalytic activity and hydrothermal temperature. By optimizing the hydrothermal growth temperature, as fabricated and supported ZnO nanosheet arrays grown at 110 °C have struck a balance between the increase in surface area and thickness, it exhibits efficient photodegradation, facile fabrication, high recyclability, and improved durability. The RhB photodegradation efficiency of optimized and grown ZnO nanosheet arrays increased by more than four times that of the unoptimized structure. With 10 cm2 of as-fabricated ZnO nanosheet arrays, the degradation ratio of 10 mg/L MO, MB, OFL, and NOR was 85%, 51%, 58%, and 71% under UV irradiation (365 nm, 20 mW/cm2) for 60 min. All the target pollutant solutions were almost completely degraded under UV irradiation for 180 min. This work offers a facile way for the fabrication and morphological control of the supported nanostructured photocatalyst with excellent photodegradation properties and has significant implications in the practical application of the supported nanostructured photocatalyst for water pollution photodegradation.

Effect of hydrothermal temperature on phase transformation and mechanical property of non-sintered hydroxyapatite and its in vitro solubility

Effect of hydrothermal temperature on phase transformation and mechanical property of non-sintered hydroxyapatite and its in vitro solubility

Adsorption of cerium (III) by zeolites synthesized from kaolinite after rare earth elements (REEs) recovery.

REE recovery tests were performed on a kaolinite and the corresponding metakaolinite using pH static leaching method. Test results show that over 90% of REEs were leached from the metakaolinite sample at pH 0.00 and 25°C, while less than 2% of the major constituents were simultaneously extracted. Therefore, selective leaching of REEs from the metakaolinite was achieved through pH static leaching. The leaching residue was then subjected to alkaline activation for zeolites synthesis. The effects of hydrothermal temperature and incubation period under various alkaline conditions on the synthesis of zeolites were systematically investigated. The phase compositions, textual properties, and morphology of the synthesized products were characterized. Pure zeolite A with 100% relative crystallinity was successfully synthesized at 80°C for 6h when using 3M NaOH as the alkaline activator. While as the synthesis conditions became increasingly harsh, the metastable zeolite A gradually transformed into more stable sodalite, and three types of zeolites, including zeolite A, sodalite, and their mixtures, were obtained. After that, various types of zeolites were applied for Ce3+ adsorption from aqueous solutions. High purity sodalite showed a higher adsorption capacity of 53mg/g at pH 6.0 and 25°C as a result of the superior textual properties compared with zeolite A. The adsorption data were suitably fitted by the Langmuir isotherm and pseudo-second-order models. Findings from this study suggest that the kaolinite is a potential source for REE recovery, and the leaching residue is suitable for the synthesis of zeolites, which can be used as promising adsorbents for Ce3+ recovery.

Synthesis of Fe3O4/C composites derived from cornstalk by one-step hydrothermal method as a reusable adsorbent for dyes

The magnetic reusable Fe3O4/C composites were prepared derived from agriculture waste cornstalk and ferric nitrate through one-step hydrothermal method. In the preparation process, ferric nitrate was used as not only source of Fe3O4 but also catalyst to promote the generation of carbon nanomaterials from cornstalk avoiding the use of alkali agents and high temperature. The effect of hydrothermal temperature on the crystallite structure and size, magnetic property, adsorption activity of Fe3O4/C composites were mainly investigated. And, the adsorption kinetics and reusability of Fe3O4/C composites were studied. The result showed that the magnetic property increased with the increase of hydrothermal temperature due to the generation of Fe3O4 nanoparticles. Meanwhile, Fe3O4 nanoparticles improved the exfoliation of carbon nanosheets resulting in the increase of the specific surface areas and decrease of the active adsorption sites. Due to both effect of the specific surface areas and active adsorption sites, the adsorbed amount of Fe3O4/C composite increased while the removal rate decreased with the increase of hydrothermal temperature. All Fe3O4/C composites exhibited good adsorption performance to MB and RhB dyes. The removal rate of MB on Fe3O4/C composite with optimum hydrothermal temperature was about 56 % after five cycles, exhibiting good reusability.

Effects of hydrothermal treatment on organic compositions, structural properties, dewatering and biogas production of raw and digested sludge

The effects of hydrothermal treatment (HTT) under different temperatures and time (120 °C to 250 °C, 10 min to 60 min) on organic matter solubilization and structure changes of secondary sludge (SS) and digested sludge (DS), as well as downstream dewatering and anaerobic digestion were investigated. The results showed that organic matter solubilization increased significantly at 120 °C to 170 °C, then decreased at 200 °C to 250 °C. The organic matter solubilization during HTT showed no obvious difference for two sludge, but for the different organic components. The polysaccharides are easier to be dissolved than protein, which was manifested by the higher dissolution rate at low temperature. The protein was the main soluble component for both of hydrothermal SS and DS, which accounted for 44 % to 64 % of soluble chemical oxygen demand (SCOD). The decrease of residual extracellular polymeric substances (EPS) content and increase of N-acetylglucosamine and DNA concentrations indicated that sludge EPS and cell wall structure were damaged at 170 °C, which contributed to the high organic matter solubilization. Nitrogen balance and molecular weight distribution indicated the concentrations of soluble organic components were the combined result of dissolution and hydrolysis reaction. The hydrolysis and polymerization reaction were intensified at 170 °C to 250 °C, which was verified by the COD balance and molecular weight transformation. The hydrothermal time could further facilitate the organics dissolution and hydrolysis based on the effect of hydrothermal temperature. The EPS structure damage also contributed to the high percentage of free moisture, resulting in enhanced dewaterability. The highest methane production was 298.1 mL CH4/g VSadd for DS hydrothermally treated at 170 °C, which were 125 % and 9.8 % higher than SS and SS-HTT, respectively. This study provided an insight into the general mechanism of HTT and the application of different HTT and AD configurations.

Hydrothermal synthesis of zeolitic material from circulating fluidized bed combustion fly ash for the highly efficient removal of lead from aqueous solution

The utilization of coal fly ash derived from circulating fluidized bed combustion (CFBFA) still faces great challenges because of its unique characteristics. In this study, a zeolitic material with Na-P1 zeolite as the main phase was successfully synthesized via a hydrothermal method by using CFBFA as the raw material. The effects of hydrothermal temperature, time, and added CTAB amount on the characterizations of synthesized materials were investigated by XRD, SEM, and XPS. The properties of the optimal zeolitic material and its adsorption performance for Pb2+ in aqueous solution were evaluated. The influences of pH, initial concentration, dosage, and temperature on Pb2+ adsorption were also examined. Results revealed the following optimal parameters for the synthesis of zeolitic material: NaOH concentration of 2 mol·L−1, solid-to-liquid ratio of 1:10 g·ml−1, hydrothermal temperature of 110 °C, hydrothermal time of 9 h, and CTAB amount of 1 g (per 100 ml solution). The adsorption capacities of the zeolitic material reached 329.67, 424.69, and 542.22 mg·g−1 when the pH values of aqueous solution were 5, 6, and 7, respectively. The Pb2+removal efficiency can reach more than 99% in aqueous solution with the initial concentrations of 100–300 mg·L−1 under pH 6 and suitable adsorbent dosage. The adsorption and kinetics of Pb2+ on the zeolitic material can be described by Langmuir isotherm and pseudo-second-order kinetic models, respectively. The ion exchange between Pb2+ and Na+ and chemisorption are the main adsorption mechanism. All these findings imply that the synthesis of low-cost adsorbent for Pb2+ removal from weak acid and neutral aqueous solution provides a highly effective method to utilize CFBFA.

Effect of CaO and hydrothermal carbonization conditions on the fuel characteristics of rice husk hydrochars.

The effects of hydrothermal temperature and catalyst concentration on the basic elements and combustion characteristics and kinetic parameters of hydrochars were investigated using ultimate analyzer and thermogravimetric method with rice husk as the research object and CaO as the additives. The results showed that: (1) the fixed carbon content of hydrochars gradually increased with the increase of hydrothermal temperature, whereas the volatile content gradually decreased. When CaO was added, the changes of fixed carbon and volatile fraction gradually decreased with the increase of hydrothermal temperature, and H/C atomic ratio increased to different degrees, which had a certain inhibitory effect on the degree of hydrothermal carbonization of rice husk. (2) The peak of the volatile fraction combustion section of hydrochars combustion derivative thermogravimetric curve was higher than that of the fixed carbon combustion section. CaO concentration has less effect on the volatile combustion section, and the combustion peak of the fixed carbon section is significantly reduced. (3) When the heating rate of the combustion test is accelerated, the ignition and burnout temperatures of the sample increase and the overall combustion curve shifts to the high temperature region. (4) The comprehensive combustion index SN decreases with the increase in hydrothermal temperature. When the hydrothermal temperature is certain, the CaO concentration causes the SN to increase and then decrease, which finally reduces the combustion performance of hydrochars. (5) The activation energy of the fixed carbon combustion section of hydrochars is lower than that of the volatile combustion section, and the activation energy of both volatile and fixed carbon combustion sections gradually decreases after adding CaO. The primary reaction kinetic model was used to describe the combustion kinetics of hydrochars, and the correlation coefficients (R2) were all above 0.92, and the results were reliable.