Hydrothermal Treatment Temperature Research Articles

Impact of Synthesis Parameters on the Crystallinity of Macroscopic Zeolite Y Spheres Shaped Using Resin Hard Templates

In this study, the effects of several synthesis parameters including aging time, micropore-structure-directing agents, and hydrothermal treatment temperature profile were systematically examined with respect to their impact on the crystallinity of macroscopic zeolite Y spheres formed in the presence of organic anion-exchange resin templates. Spherical resins were utilized as hard templates to shape the zeolite Y particles. Zeolite Y precursors were initially deposited into the pores of the resin template and subsequently crystallized over time through precise control over these synthesis parameters. The resulting zeolite Y spheres were characterized using an array of characterization techniques, including XRD, SEM, TEM, BET, FTIR, and XRF. We identify the optimal conditions for maximizing the crystallinity of the macroscopic zeolite Y particles using resin templates as macroscopic shaping agents. This functional material has the potential to be used as both catalyst and adsorbent in several applications.

Multilayer-coating process for the synthesis of nickel-silicate composite with high Ni loading as high-rate performance lithium-ion anode material

BackgroundMetal silicates possess several important advantages as electrode materials for lithium-ion batteries (LIBs), including straightforward synthesis, low cost, and high thermal stability. A green synthesis routes that are capable of increasing metal loading and reducing the impact on the environment are required. MethodsA Ni-silicate with a multilayer structure and a Ni/Si molar ratio of 0.25 is first prepared using the co-precipitation method. The as-synthesized product is then repeatedly immersed in a Ni2+ solution to obtain Ni-silicate with the desired Ni contents (Ni/Si molar ratio: 0.50–2.00). Finally, the resulting Ni-silicate is reconstructed by hydrothermal treatment under various temperatures (70 °C, 100 °C, 150 °C) and durations (3 h and 24 h) to obtain Ni-phyllosilicate. The effects of the hydrothermal treatment temperature, hydrothermal time, and Ni/Si ratio on the structure, morphology, and surface area of the Ni-silicate composites are examined. Significant FindingsThe Ni-silicate with a Ni/Si ratio of 1.5 has a reversible capacity of 729 mAhg-1, which exceeds traditional graphite anodes (372 mAhg-1). Furthermore, the material exhibits a capacity retention of up to 80 % as the current density is increased from 0.025 Ag-1 to 0.5 Ag-1. Thus, the synthesized Ni-silicate composite is a promising candidate material for LIB anode.

Macroscale properties and atomic-scale mechanisms of ash removal in low-temperature hydrothermal carbonization

Biogenic ash is a significant impediment to the utilization of agricultural residues in biofuel production. Such challenge can be addressed by various treatments, as demonstrated in this study on the experimental and computational mechanisms involved in the hydrothermal treatment (HT) of wheat straw. A combination of classical (all-atom) molecular dynamics simulations of cellulose carrying silica and calcium species, along with first principles quantum chemical calculations, indicates the dissociation of inorganics from the cellulose with increased HT temperature. This observation is confirmed by experimental evidence of effective ash removal by HT, showing at least 50% removal of sulfur, chlorine, potassium, and calcium, and 12.5% of silica, leading to a reduced total ash content (from 6.7% to 4.2%).Changes in structural features upon HT, such as surface cellular structure and porosity, were revealed, accompanied by an increased specific surface area (from 1.17 to 6.34 m2/g). Our simulations suggest that silica binds tightly to the hydrophobic face of cellulose at room temperature, but HT significantly reduces the binding free energy of association with both hydrophobic and hydrophilic surfaces. Most significantly, ash removal leads to an increased calorific value, rising from approximately 16 MJ/kg to about 19 MJ/kg, along with improved thermal behavior. The improved integration combustion index parameter S indicates that the combustion properties improve with ash removal efficiency. The proposed atomic-level mechanism for the observed removal of inorganics during mild HT underscores the potential of such treatment in producing energy-dense wheat straw, a widely available agricultural residue.

From mixed brookite/anatase TiO2 nanopowder to sodium titanates: Insight into morphology, structure, and photocatalytic performance

A method to obtain sodium titanate nanoribbons starting from a mixture of brookite and anatase TiO₂ nanopowder is described. As-prepared TiO2 nanopowder with a major brookite phase was used as a precursor in an alkaline hydrothermal approach, where the temperature was kept at 200 °C. The influence of hydrothermal treatment and consequent annealing temperature (T = 500 °C) on the crystal structure, phase composition, and morphology of samples were investigated by X-ray powder diffraction (XRPD), Raman and FTIR spectroscopy, and electron microscopy techniques (FESEM, HRTEM). All these methods point out that the hydrothermally treated sample, containing the NaTi3O6(OH)(H2O)2, Na2Ti3O7, and Na2Ti9O19, is dominated by layer-structured sodium hydroxititanate dihydrate. The annealing leads to the formation of rare sodium titanates, Na3Ti6O13 and Na2Ti9O19, with tunnel structures where the hexatitanate with increased sodium content prevails. The photocatalytic activity of synthesized nanostructures was tested in the degradation process of Reactive Orange (RO16) azo-dye upon UV excitation. It appears that photocatalytic activity is lower after hydrothermal treatment, but subsequent annealing makes sodium titanate nanoribbons faster in the degradation of RO16. The research implies that these sodium titanate nanostructures are promising photocatalytic materials and should be considered in the future for removing different pollutants from water.

Flexural properties of moso bamboo induced by hydrothermal treatment

The superior flexural properties of bamboo make it widely used in the field of bamboo furniture. However, thick bamboo strips are more susceptible to fracture in bending due to their significant fiber gradient variation, especially the nodes. In this study, the eco-friendly hydrothermal treatment was employed to augment the flexural properties of bamboo and mitigate the fracture. The results showed that the flexural strength, flexural modulus, flexural toughness, and flexural radius of curvature increased with the increase of strip thickness. The strip thickness was positively correlated with vascular bundle content. The structure of bamboo became more uniform after hydrothermal treatment and the nodes were no longer the susceptible fracture point. The moisture content was a pivotal factor influencing the flexural properties, which increased as hydrothermal treatment time and temperature increased. Furthermore, hydrothermal treatment increased bamboo's flexibility by softening it through moisture absorption and the facilitating molecular chain movement within the fibers. The optimal moisture content for bamboo strips when manufacturing curved components was around the fiber saturation point. These findings contributed to the refinement of the green manufacturing techniques for bamboo curved furniture components, aiming to foster sustainable environmental development.

Multi-component attached carbon matrix composites with superior electromagnetic wave absorption performance and multifunctional applications

The preparation of highly absorbing and high-performance electromagnetic wave-absorbing materials remains a significant challenge. In this paper, carbon matrix composites modified with sodium inorganic salts (CMS) have been successfully prepared by using the solvent evaporation method in combination with the hydrothermal treatment and high temperature carbonization processes. The composition of the product can be manipulated by varying the material ratios, which in turn affects the interface and dielectric properties of the material. Sodium carbonate (Na2CO3) was produced as a transition phase between sodium silicate and carbon matrix due to high temperature. According to differential charge density a significant charge accumulation found between the interfacial of Na2CO3 and carbon layer is helpful to polarization. The synergistic effect of polarization and conduction loss due to the formation of multiple heterogeneous interfaces and carbon matrix results in excellent electromagnetic wave absorption performance. The minimum reflection loss (RLmin) is −55.49 dB when the thickness is 3.1 mm. Furthermore, CMS composites exhibit notable flame retardancy and thermal insulation properties, rendering them suitable for a diverse range of applications. These remarkable achievements provide new ideas for the design and development of efficient electromagnetic wave absorption materials.

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.

THE INFLUENCE OF THE HYDROTHERMAL LIGNIN CARBONISATION TEMPERATURE ON THE PROPERTIES OF BIOCHAR AS A POTENTIAL SOLID FUEL

The effect of hydrothermal carbonisation temperature (190-250 °C) on the properties of biochar produced from hydrolytic lignin was studied. Biochar was investigated using a set of physicochemical methods; its elemental, proximate and thermal analysis was carried out. It is shown that an increase in the temperature of hydrothermal treatment has a negative effect on biochar yield but allows obtaining a more thermally stable product with fuel characteristics comparable with those of brown coal.

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.