Hydrothermal Treatment Temperature Research Articles

WITHDRAWN: Component Analysis of Corncob after Hydrothermal Treatment

Hydrothermal pretreatment is a green pretreatment technology, which can effectively promote the degradation of biomass without adding any chemical reagent. In this study, hydrothermal pretreatment on improving digestibility of corncobs was investigated and the effect of hydrothermal pretreatment on changes of structure of the corncob lignocellulose was investigated. The composition and amounts of sugar content in hydrolysate and enzymatic hydrolysate were determined. Hydrothermal treatment destroyed the lignocellulose structure of corncob and caused different degrees of degradation. With the increasing temperature of hydrothermal treatment, the degradation of cellulose, hemicellulose and lignin in corncob was detected with increasing the content of reducing sugars in hydrolysate. The hydrolysate of corncob treated by hydrothermal treatment at 190 ℃ for 60min mainly included glucose, xylobiose, xylotriose and xylotetraose. The content of glucose, xylobiose, xylotriose and xylotetraose in the hydrolysate of hydrothermal treatment corncob was at level of 0.001mg·g-1, 16.740mg·g-1, 4.306mg·g-1 and 3.164mg·g-1 respectively. The yield of glucose, xylobiose, xylotriose and xylotetraose in enzymatic hydrolysate were 4.771mg·g-1, 64.437mg·g-1, 6.853mg·g-1 and 1.835mg·g-1, respectively. The understanding will help to improve the conversion and utilization of corncob as an agriculture residue.

Rapid Waste Motor Oil Conversion into Diesel-Range Hydrocarbons Using Hydrochar as Catalyst: Kinetic Study and Product Characterization

Herein, raw and alkali-treated hydrochars from biomass waste are prepared as a highly active catalyst for the conversion of waste motor oil into diesel-like fuels. Among all materials, hydrochar obtained at 250 °C and subsequent alkali activation with KOH showed a 600% improvement of the kinetic constant from 0.0088 to 0.0614 m−1. Conversion values at the same conditions were also improved from 66 to 80% regarding thermal and catalytic cracking, respectively. Moreover, the activation energy was also reduced from 293 to 246 kJ mol−1 for thermal and catalytic cracking, respectively. After characterization, the enhanced catalytic activity was correlated to an increased surface area and functionalization due to the alkali activation. Finally, the liquid product characterization demonstrated that catalytic cracking is more effective than thermal cracking for producing hydrocarbons in the diesel range. In particular, hydrochar-based catalysts are suggested to promote the formation of specific hydrocarbons so that the carbon distribution can be tailored by modifying the hydrothermal treatment temperature.

Effect of hydrothermal treatment on the rheological properties of xanthan gum

In this study, the effect of hydrothermal treatment with different temperatures (120–180 °C) on the rheological properties of xanthan gum was evaluated. When the temperature of hydrothermal treatment was relatively low (120 °C), the rheological properties of the hydrothermally treated xanthan gum was similar to the untreated xanthan gum (pseudoplastic and solid-like/gel-like behavior). However, as the temperature of hydrothermal treatment was higher, the rheological properties of the hydrothermally treated xanthan gum changed greatly (e.g., a wider range of Newtonian plateaus in flow curves, existence of a critical frequency between the storage modulus (G') and the loss modulus (G") in the dynamic viscoelasticity measurement, variation of complex viscosity). Although the hydrothermal treatment showed little influence on the functional groups of xanthan gum, it altered the micromorphology of xanthan gum from uneven and rough lump-like to thinner and smoother flake-like. In addition, higher concentration (2 %) of hydrothermally treated xanthan gum made its viscosity close to that of the untreated xanthan gum (1 %). Besides, hydrothermal treatment also affected the effect of temperature and salt (CaCl2) adding on the rheological properties of xanthan gum. Overall, this study can provide some useful information on the rheological properties of xanthan gum after hydrothermal treatment.

Mechanism insights into hydrothermal-activated tannic acid (TA) for simultaneously sewage sludge deep dewatering and antibiotics removal

Tannic acid (TA) aided hydrothermal treatment (HT) can decrease effective HT temperatures for sludge deep dewatering by chelator protein, but faces notable and economic challenges including the failure to remove antibiotics and the limited protein binding capacity. Herein, hydrothermally activated TA (in situ TA + HT) was conducted to simultaneously improve sludge dewaterability and antibiotic (tetracycline (TC), oxytetracycline (OTC), norfloxacin (NOR), ofloxacin (OFL)) removal. Compared to traditional HT and HT + TA treatment, the in-situ TA + HT process could further strengthen the TA-aided HT efficacy in enhancing sludge and reducing the protein content in the filtrate simultaneously; in which the optimal HT temperature for the dewatering of the sludge was reduced from 180 °C to 140 °C. Furthermore, the total removal efficiency of target antibiotics was achieved at more than 71.0–94.7% for TC and OTC, and 72.0–84.8% for NOR and OFL. The highly reactive species (·OH) generation and the electron transfer efficiency from the hydrothermal-activated TA process were responsible for the elimination of antibiotics and promoted the hydrolyzation and mineralization of HMW protein in sludge during the HT process. Meanwhile, the degradation of HMW proteins and the destruction of the secondary structure of these proteins resulted in improved hydrophobicity and dewaterability of sludge. Hydrothermally activated TA induces covalent binding with the protein. As a result, hydrothermal-activated TA could promote the removal of antibiotics and proteinaceous compounds from the sludge samples, improving the hydrophobicity of sludge and releasing bound water from the sludge flocs during HT. Finally, the cost of hydrothermal-activated TA was 66.51% lower than that of thermal drying treatment. This study not only proposed an effective method to improve traditional HT for sludge thermal dry-free treatment, but also provided new information on the catalysis roles of polyphenols in the hydrothermal conversion of sludge.

Component Analysis of Corncob After Hydrothermal Treatment

Hydrothermal pretreatment is a green pretreatment technology, which can effectively promote the degradation of biomass without adding any chemical reagent. In this study, hydrothermal pretreatment on improving digestibility of corncobs was investigated and the effect of hydrothermal pretreatment on changes of structure of the corncob lignocellulose was investigated. The composition and amounts of sugar content in hydrolysate and enzymatic hydrolysate were determined. Hydrothermal treatment destroyed the lignocellulose structure of corncob and caused different degrees of degradation. With the increasing temperature of hydrothermal treatment, the degradation of cellulose, hemicellulose and lignin in corncob was detected with increasing the content of reducing sugars in hydrolysate. The hydrolysate of corncob treated by hydrothermal treatment at 190 °C for 60 min mainly included glucose, xylobiose, xylotriose and xylotetraose. The content of glucose, xylobiose, xylotriose and xylotetraose in the hydrolysate of hydrothermal treatment corncob was at level of 0.001 mg • g−1, 16.740 mg • g−1, 4.306 mg • g−1 and 3.164 mg • g−1 respectively. The yield of glucose, xylobiose, xylotriose and xylotetraose in enzymatic hydrolysate were 4.771 mg • g−1, 64.437 mg • g−1, 6.853 mg • g−1 and 1.835 mg • g−1, respectively. The understanding will help to improve the conversion and utilization of corncob as an agriculture residue.

Effect of Hydrothermal Treatment on the Mechanical and Microscopic Properties of Moso Bamboo

In this study, moso bamboo was used as a raw material. To increase the plasticity of bamboo to achieve a greater softening effect, the softening method of hydrothermal treatment was used. Hardness and the flexural elastic modulus were used as the evaluation indices, and the crystallinity and main functional groups of the softened bamboo were analysed using X-ray diffraction and Fourier-transform infrared spectroscopy. Combined with the examination of timber colour, micromorphology, bending strength, and nanomechanical tests, our analysis showed the effects of the hydrothermal treatment on bamboo. The results showed that the hardness and flexural moduli of bamboo decreased with the increase in hydrothermal treatment temperature. However, cracking occurred after 3.5 and 4 h of treatment at 180 °C and 190 °C. This indicated that the softening effect was most pronounced when the treatment temperature and time were 180 ℃ and 3 h, respectively. The cellulose crystallinity of bamboo increased and then decreased with the increase in treatment temperature. Cracks were produced in the cell structure, starch locally disappeared, and the hardness and the elasticity modulus of the thin-walled bamboo cells first increased and then decreased with the increase in treatment temperature.

The pretreatment and enzymatic hydrolysis behaviors of lignocellulosic biomass (oak and larch) based on structural changes in its lignin-carbohydrate complex

This study investigated the structural changes in oak and larch lignin-carbohydrate complexes (LCCs) during hydrothermal treatment and enzymatic hydrolysis. Hydrothermal treatment caused hemicellulose degradation (degradation rate at 170 ℃: larch 19.40%; oak, 22.26%). The LCC1 (glucan-lignin) fraction was the highest in the raw material of both biomasses. The LCC3 (xylan-lignin) and LCC2 (glucomannan-lignin) fractions were high in oak and larch, respectively; these fractions decreased as the hydrothermal treatment temperature increased (owing to hemicellulose degradation). Both biomasses had phenyl glycoside, benzyl ether (BE), and γ-ester (Est) linkages. The BE and Est linkages decreased as the hydrothermal treatment temperature increased; the Est linkages decrease was more significantly in oak than in larch. The efficiency of enzymatic hydrolysis was higher in oak than that in larch and increased as the hydrothermal treatment temperature increased. Furthermore, enzyme adsorption on the LCC1 sensor was higher in oak than in larch. The chemical compositions and LCC linkages of the biomass were changed by the hydrothermal treatment, which affected the efficiency of enzymatic hydrolysis. Moreover, the efficiency of enzymatic hydrolysis was higher for oak than for larch because of the difference hemicellulose and cellulose contents and LCC linkages.

Synthesis of zeolite materials based on dispersed microspheres from fly ash from coal combustion and their sorption properties in relation to Pb(II) and Cd(II)

The influence of the composition of two narrow fractions of dispersed microspheres from fly ash from coal combustion and synthesis conditions on the production of microspherical monozeolite materials of a certain structural type was studied. The possibility of using synthesis products as Pb2+ and Cd2+ sorbents was assessed. It has been established that zeolitization products based on microspheres with a high content of glass phase (more than 90 wt. %) are monolithic solid materials of the geopolymer type, consisting of agglomerated microsphere residues and zeolite phases and, depending on the synthesis temperature, contain mainly one zeolite phase – NaX (FAU), NaP1 (GIS) or analcime (ANA). A simultaneous increase in the alkali concentration and the temperature of hydrothermal treatment led to a deeper transformation of glass microspheres and partial agglomeration of product particles with the formation of granules up to 100 microns in size. The product of alkaline activation of microspheres with a lower glass phase content (~65 wt. %) is a dispersed material based on unreacted microspheres, zeolite phases, mullite and quartz. Most zeolite products in the low Pb2+ and Cd2+ concentration range (not higher than 20 mg/l) were characterized by high solution purification parameters – KD up to 105 ml/g, the degree of extraction was up to 99%, while the most effective were sorbents based on zeolite phases NaP1 and analcime. Sorption isotherms of Pb2+ and Cd2 were approximated using the Langmuir, Freundlich, and Dubinin-Radushkevich models. It has been established that the sorption of heavy metals from dilute solutions is best described by the Freundlich and Dubinin-Radushkevich models. It has been shown that Pb2+/Cd2+ exchange forms of zeolite materials as a result of thermal exposure at 1000 оC undergo a phase transformation with the formation of mineral-like feldspar phases including lead (PbAl2Si2O8) or cadmium (CdAl2Si2O8).

Composition of Hydrocarbon Gases Formed by Dry Pysolysis of Domanik Shale Kerogen after Hydrothermal Experiment

The composition of hydrocarbon gases formed by pyrolysis of residual Domanik shale kerogen at 800°C, preceded by hydrothermal treatment at 250–375°С, was studied by pyrolytic gas chromatography. Starting from the autoclave temperature of 320–325°C, the hydrothermal treatment of the shale affects the kerogen structures responsible for the formation of C2+ gases in pyrolysis at 800°C. An increase in the temperature of the shale hydrothermal treatment leads to a monotonic increase in the С1/С2+ ratio in the products of the residual kerogen pyrolysis at 800°C. The methane yield at 800°C does not correlate with the content of alkyl structures, determined in kerogen by IR spectroscopy, and the yield of С2+ gases linearly correlates with the content of alkyl structures.

Applying sludge hydrolysate as a carbon source for biological denitrification after composition optimization via red soil filtration

Sludge hydrolysate, the byproduct generated during sludge hydrothermal treatment (HT), is a potential carbon source for biological denitrification. However, the refractory organic matters and the nutrient substances are unfavorable to the nitrogen removal. In this study, effects of HT conditions on the hydrolysate properties, and the hydrolysate compositions optimization via red soil (RS) filtration were investigated. At HT temperature of 160–220 °C and reaction time of 1–4 h, the highest dissolution rate of organics from sludge to hydrolysate achieved 70.1 %, while the acetic acid dominated volatile fatty acids (VFAs) was no more than 5.0 % of the total organic matter content. The NH4+-N and dissolved organic nitrogen (DON) were the main nitrogen species in hydrolysate. When the hydrolysate was filtered by RS, the high molecular weight organic matters, DON, NH4+ and PO43− were effectively retained by RS, while VFAs and polysaccharide favorable for denitrification were kept in the filtrate. When providing same COD as the carbon source, the filtrate group (Fi-Group) introduced lower concentrations of TN and humic substances but higher content of VFAs. This resulted in TN removal rate (57.0 %) and denitrification efficiency (93.6 %) in Fi-Group higher than those in hydrolysate group (Hy-Group), 39.4 % and 83.7 %, respectively. It is noticeable that both Hy- and Fi- Groups up-regulated most of denitrification functional genes, and increased the richness and diversity of denitrifying bacteria. Also, more denitrifying bacteria genera appeared, and their relative abundance increased significantly from 3.31 % in Control to 21.15 % in Hy- Group and 31.31 % in Fi-Group. This indicates that the filtrate is a more suitable carbon source for denitrification than hydrolysate. Moreover, the pH rose from 4.6 ± 0.14 to 6.5 ± 0.05, and the organic carbon, TN, TP and cation exchange capacity (CEC) of RS increased as well after being filtered, implying that the trapped compounds may have the potential to improve soil quality. This study provides a new insight for hydrolysate application according to its composition characteristics, and helps make the most use of wasted sludge.

Roles of extracellular polymeric substances in the adsorption and removal of norfloxacin during hydrothermal treatment of sewage sludge

Hydrothermal treatment (HT) is promising to remove antimicrobials from sewage sludge (SS); however, the mechanism of antimicrobial degradation during the HT of SS is not fully understood. In this study, the roles of extracellular polymeric substances (EPS) in the removal and transformation of norfloxacin (NOR) during the HT of SS at temperatures of 100 and 160 °C were investigated. The results indicated that the degradation of NOR increased with increasing HT temperature, with maximum NOR removal (52%) achieved at 160 °C. Furthermore, the NOR in sludge showed higher degradation efficiencies than the control as HT temperature was higher than 120 °C. Evident promotion effects of bound-EPS (B-EPS) in sludge were observed on the NOR degradation as HT temperature was higher than 120 °C, leading to the mineralization and deamination of protein-like components in EPS during HT. Beside, the adsorption capacity of NOR during the HT of SS decreased at temperatures higher than 120 °C. The evolution of the spatial structure of B-EPS was predominantly responsible for the adsorption of antimicrobials, a spontaneous process driven mainly by hydrophilic interactions. With the hydrothermal conversion of B-EPS, the electron transfer, and reactive species (3EPS* and ·OH) derived from B-EPS could facilitate the degradation of NOR. In particular, hydrogen bonds between B-EPS and NOR increased the apparent yield of ·OH and accelerated the decarboxylation of NOR during HT at temperatures higher than 120 °C. A toxicity evaluation suggested that HT for NOR degradation could attenuate toxicity, whereas deep oxidation or mineralization would be needed to promote ecosystem safety. These findings provide new insights into the hydrothermal activation of EPS and the interrelated hydrothermal fate of antimicrobials and other toxic pollutants in sludge.

Synergistic effects of hydrothermally decorated Ag nanoparticles over rGO for antibacterial activities

Antibacterial activity of the silver decorated reduced graphene oxide (Ag-rGO) nanocomposites have been investigated against E. coli as a model for gram-negative bacteria. The effect of temperature during the hydrothermal treatment of Ag-rGO nanocomposites synthesized by simultaneous reduction of GO and AgNO3 over the antibacterial activity has been studied. The composite samples were further reduced hydrothermally at different temperatures, viz. 100 °C, 150 °C, and 200 °C for 24 h to integrate silver nanoparticles (AgNPs) into rGO. Variations in the hydrothermal treatment temperature allowed alterations in the morphology and particle size of the AgNPs. The AgNPs grown at room temperature are in bunches and smaller sizes, whereas the hydrothermally treated samples have uniformly distributed bigger AgNPs. The particle size of AgNPs on rGO grows from 45 nm at room temperature to 65 nm and 220 nm in the hydrothermally treated samples at 150 °C and 200 °C, respectively. The antibacterial activity of the Ag-rGO composite has been observed to be size dependent. The Ag-rGO composite hydrothermally treated at 150 °C, having a particle size of ∼65 nm, has been observed to have the highest activity; the zone of inhibition is 3.4 ± 2.8 cm. The Ag nanocrystallite’s edges and defects in the rGO sheets together destroy the bacterial cells in a series of stages, ultimately resulting in cell death and high antibacterial activity.

Tailored chemical modification of ZSM-5 zeolite supports for Mo-based catalysts optimized for methane dehydroaromatization: Hydrothermal dealumination was key to improving the selectivity of desired aromatic compounds

In this study, we considered Mo-impregnated H-ZSM-5 zeolite catalysts (denoted by Mo/Z) for methane dehydroaromatization (MDA). In particular, we attempted to reduce the amount of Brønsted acid sites (BAS) of the H-ZSM-5 supports via hydrothermal dealumination to disfavor the final product of the MDA (i.e., coke) and, thus, improve the intermediate aromatic compounds (mainly, benzene and toluene: BT). In fact, the hydrothermal treatment of H-ZSM-5 supports at ca. 400 °C prior to Mo-impregnation (the resulting catalyst is denoted by Mo/Z_400) improved the BT formation rates over the 12-h reaction relative to Mo/Z. In particular, coke analyses on the spent catalysts recovered after different reaction times revealed that Mo/Z_400 suppressed the formation of hard coke fractions and, accordingly, increased the intermediate BT products, as compared to Mo/Z. For this, thermogravimetric analysis complemented with micropore analysis clearly indicated that the chemically modified property (here, BAS), not the physical counterpart (here, 10-membered-ring micropores), was key to achieving such activity and, furthermore, their gradual decrease could account for the deactivation behavior as a function of time. In addition, the coke formed outside was likely to contribute to the deactivation as well. However, higher hydrothermal treatment temperatures (500, 600, or 700 °C) rather deteriorated the catalytic activity, suggesting that extensive dealumination of the zeolite framework resulted in the excessive loss of desired BAS. Such improvement based on the optimal modification of BAS allowed for competitive MDA performance to be as good as those of other complex post-processed, high-performance Mo-based ZSM-5 zeolites reported in the literature.

Inhibition insights of hydrothermal liquid digestate in anaerobic digestion: Impact on organics conversion and inhibitor degradation

Hydrothermal liquid digestate has been widely accepted as a substrate in anaerobic digestion (AD) for energy recovery. However, the potential negative impacts of hydrothermal liquid digestate on AD remain unclear. In this study, the organic biodegradability of hydrothermal liquid digestate produced from hydrothermal treatment (HTT) at different temperatures was analyzed, and the formation and degradation process of potential inhibitory substances were discussed. Results demonstrated that the AD lag phase of hydrothermal liquid digestate increased from 3 days at raw liquid digestate to 5–21 days. When the HTT temperature reached 220 °C, the methane yield decreased by 48%, and more than 71% of the organics in the hydrothermal liquid digestate were not utilized by AD. Biorefractory substances, such as fulvic and humic acids, accumulate in the hydrothermal liquid digestate. Potential inhibitory substances from Maillard reactions mainly affect the methanogenesis of AD. Most inhibitory substances were degraded within 7–22 days, with the degradation rate following the order of pyrroles > pyrazines > ketones > imidazoles > indoles. The AD community structure and methane conversion were partially re-established after most inhibitory substances were degraded. This study provides valuable information on eliminating the potential negative effects of hydrothermal liquid digestate on AD.

Tailoring the electronic structure of Ni5P4/Ni2P catalyst by Co2P for efficient overall water electrolysis

The advancement of highly-active bifunctional electrocatalysts towards hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is imperative for reducing costs and improving efficiency. Phosphides, as the representative of bifunctional catalysts, can be used for HER and OER by virtue of the special metal/phosphorus coordination mode and the ordered surface reconstruction. However, the inappropriate adsorption/desorption energy for intermediates, poor reaction kinetics and scant activation analysis limit their large-scale application. Here, we developed a novel Ni/Co phosphide multi-component heterostructure catalyst on Ni foam (Co2P/NixPy@NF) through hydrothermal treatment and low temperature phosphorization. Benefitting from open hierarchical structures, abundant active sites, rapid mass/charge transfer rates, and modified electronic structures, the optimal catalyst exhibits excellent activity and high stability towards HER (155 mV overpotential in 1.0 M KOH and 175 mV overpotential in 0.5 M H2SO4 at 100 mA·cm−2), OER (300 mV in 1.0 M KOH at 100 mA·cm−2), and overall water electrolysis (1.74 V cell voltage in 1.0 M KOH at 100 mA·cm−2). Post-stability analysis further reveals that hydroxide and oxyhydroxide are generated on catalysts' surfaces during HER and OER, respectively, in alkaline electrolytes. These activation processes result in the catalysts' surfaces forming new heterostructures which reorganize the electronic structure. These morphology optimizations, heterostructure engineering and investigation of activation reported here have been effective strategies for designing and exploring hybrid materials as fabulous catalysts to generate renewable energy.

Hazelnut (Corylus avellana L.) shells as a potential source of dietary fibre: impact of hydrothermal treatment temperature on fibre structure and degradation compounds.

Hemicellulose extraction from lignocellulosic biomasses has gained interest over the years, and hydrothermal treatment is one of the most common methods employed for this purpose. This work aimed to deeply study hazelnut (Corylus avellana L.) shells as a new source of dietary fibre, evaluating the effect of hydrothermal treatment temperatures on the type and structure of fibre extracted, but also on the formation of side-products derived from lignocellulose degradation. Different process temperatures led to diverse polysaccharides in the hydrothermal extract. Pectin was identified for the first time in hazelnut shells when experimenting with extraction at 125 °C, whereas at 150 °C a heterogeneous mixture of pectin, xylan, and xylo-oligosaccharides was present. The highest yield in terms of total fibre was gained at 150 and 175 °C, and then decreased again at 200 °C. Finally, more than 500 compounds from different chemical classes were putatively identified and they appeared to be present in the extracted fibre with a different distribution and relative amount, depending on the heat treatment severity. A generally high content of phenols, phenyls, oligosaccharides, dehydro-sugars, and furans was observed. Modulation of the hydrothermal treatment temperature allows fibre extracts with very different compositions, and therefore different potential end uses, to be obtained from hazelnut shells. A sequential temperature-based fractionation approach, as a function of the severity of the extraction parameters, can also be considered. Nevertheless, the study of the side-compounds formed from lignocellulosic matrix degradation, as a function of the applied temperature, needs to be fully addressed for a safe introduction of the fibre extract within the food chain. © 2023 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

TiO2 NPs-immobilized silica granules: New insight for nano catalyst fixation for hydrogen generation and sustained wastewater treatment.

In heterogeneous catalytic processes, immobilization of the functional material over a proper support is a vital solution for reusing and/or avoiding a secondary pollution problem. The study introduces a novel approach for immobilizing R25 NPs on the surface of silica granules using hydrothermal treatment followed by calcination process. Due to the privileged characteristics of the subcritical water, during the hydrothermal treatment process, the utilized R25 NPs were partially dissolved and precipitated on the surface of the silica granules. Calcination at high temperature (700°C) resulted in improving the attachment forces. The structure of the newly proposed composite was approved by 2D and 3D optical microscope images, XRD and EDX analyses. The functionalized silica granules were used in the form of a packed bed for continuous removal of methylene blue dye. The results indicated that the TiO2:sand ratio has a considerable effect on the shape of the dye removal breakthrough curve as the exhaustion point, corresponding to ~ 95% removal, was 12.3, 17.4 and 21.3 min for 1:20, 1:10 and 1:5 metal oxides ratio, respectively. Furthermore, the modified silica granules could be exploited as a photocatalyst for hydrogen generation from sewage wastewaters under direct sunlight with a good rate; 75×10-3 mmol/s. Interestingly, after the ease separation of the used granules, the performance was not affected. Based on the obtained results, the 170°C is the optimum hydrothermal treatment temperature. Overall, the study opens a new avenue for immobilization of functional semiconductors on the surface of sand granules.

Formation and growth of anatase TiO2 nanocrystals under hydrothermal conditions

This work is devoted to the study of the processes of formation and growth of TiO2 nanoparticles under hydrothermal conditions. TiO2 nanocrystals were obtained during the dehydration of hydrated titanium dioxide by varying the temperature and duration of hydrothermal treatment, as well as the method of precipitation of the synthesis precursor. The study of various characteristics of the synthesized TiO2 nanoparticles by PXRD, SEM, TEM, and low-temperature nitrogen sorption made it possible to propose mechanisms for the formation of crystalline titanium dioxide from an X-ray amorphous precursor and the growth of titanium dioxide nanocrystals with an anatase structure under hydrothermal conditions. Within the scope of the chosen model of oriented attachment, the dependence of the sizes of TiO2 crystallites on the parameters of hydrothermal synthesis is mathematically described. It was concluded that the direct precipitation of the synthesis precursor from titanium tetrachloride is superior to the reverse. It is shown that the temperature of hydrothermal treatment largely determines the size and morphology of the formed crystallites and TiO2 nanoparticles, the rate of the crystallization process, and the preferred mechanisms of nanocrystal growth, while the duration of synthesis affects the agglomeration processes and the specific surface area of titanium dioxide powders.

Long-and short-range structure of SnO2 nanoparticles: Synthesis and photo(electro)catalytic activity

We report herein a detailed study on the influence of hydrothermal treatment temperature on both long- and short-range structures of SnO2 nanoparticles (NPs) applied as photocatalysts for the discoloration of organic pollutants and as photoanodes for water splitting. Synchrotron X-ray diffraction and X-ray absorption near-edge spectroscopy measurements confirmed the enhancement of the structural order of SnO2 NPs as a function of hydrothermal temperature. Fourier transform infrared spectroscopy revealed that the hydrothermal treatment increased the amount of hydroxyl groups on the SnO2 NPs surface. Regarding the photocatalytic activity, the NPs were able to promote the discoloration of different dyes that can act as potential organic pollutants. The photoelectrocatalytic performance of the samples depended on the hydrothermal treatment temperature, with the degree of crystallinity and surface hydroxyl groups playing a significant role in their performance as photoanodes. In particular, the NPs treated at a higher temperature presented a better degree of crystallinity, in addition to many hydroxyls on their surface, leading to increased mobility of the photogenerated charge carriers and improving the interaction between the molecules degraded and the material surface. The results demonstrated that the hydroxyls adsorbed on the SnO2 surface favor the formation of hydroxyl radicals, a species that indirectly participate in the photocatalytic oxidation of rhodamine B dye. The photoelectrocatalytic tests showed that the NPs treated at 200 °C increased oxygen evolution reaction performance.

Effect of hydrothermal treatment on the surface characteristics and bioactivity of HAP based MAO coating on Ti-6Al-4V alloy

In this paper, the effects of hydrothermal treatment temperature and time on the surface characteristics and bioactivity of MAO coating on Ti-6Al-4V alloy were systematically investigated. The results showed that the amount of HAP formation on MAO coating gradually increased with the increase of hydrothermal treatment temperature and time. However, excessive temperature and time will cause the HAP pulverization on the MAO coating and cover its pores, which will be detrimental to osseointegration. It was found that when the hydrothermal treatment temperature and time were 200 °C and 24 h, respectively, the formed HAP could not be pulverized off, but could completely cover the MAO coating and retain its porous structure. Further bioactivity testing in simulated body fluid (SBF) revealed that the hydrothermally treated MAO coating generated more HAP crystal structures and covered a wider area than the sample without hydrothermal treatment. In addition, HAP first forms granules to fill the coating surface during the growth process. Then, with time HAP gradually embeds inside the coating and starts a new round of generation and fusion.