Alkaline Hydrothermal Process Research Articles

Adsorption characteristics of coal gasification fine slag with alkali-dissolution and hydrothermal treatment on methylene blue

ABSTRACT The resource utilization of coal gasification fine slag (FS) and the harmless treatment of dyeing wastewater are crucial for establishing a zero-emission industrial system and a circular economy. This study used FS as raw material and divided it into two particle sizes through ultrasonic pretreatment enhanced wet sieving. The composite materials were synthesized via an alkaline hydrothermal process from different components in FS was compared, and applied as adsorbents for the removal of methylene blue from printing and dyeing wastewater. Finally, the kinetic and thermodynamic model developed for MB from printing and dyeing wastewater. The maximum adsorption of MB by the composite material prepared from low carbon component (<0.125 mm) could reach more than 180 mg·g−1. The research results have important theoretical and practical value for guiding the high-value utilization of FS and its application in dye wastewater treatment.

Surface properties of nano‐TiO2 synthesized from two different TiO2 precursor sources by an alkaline hydrothermal process followed with a H2O2 treatment: Experiments combined with statistical analysis

AbstractOur research aimed to improve the surface properties of TiO2 for application in dye‐sensitized solar cells (DSC) by an alkaline hydrothermal process combined with H2O2 treatment. The effect of the TiO2 sources on the product quality was evaluated further by statistical analysis of the experimental data. The two commercial TiO2 precursors from Supelco (Merck – Germany) and BA‐100 (China) were used to produce nano TiO2 by the hydrothermal process in NaOH solution with two different concentrations of 5 M and 8 M at 150oC. The final products were characterized by XRD, FT‐IR, FE‐SEM, and chemical bonds on the TiO2 surface were particularly identified by XPS. The XPS data were then analyzed statistically by the K‐Means Clustering algorithm based on R software. The results showed that NaOH concentrations were directly involved with the formation of Ti─O; Ti─OH bonds and TiO2 morphology. The H2O2 treatment showed similar effects on TiO2 surface bonding but with less significant impacts than those of NaOH. In particular, the TiO2 reactant sources did not influence the structures, morphologies, and especially the surface properties of the products. Hence, a low‐cost TiO2 reactant should be selected in terms of economically effective products. The final TiO2 products were suitable for applications in DSC.

Synthesis of zeolite A and zeolite X from electrolytic manganese residue, its characterization and performance for the removal of Cd2+ from wastewater

Electrolytic manganese residue (EMR) can cause serious environmental and biological hazards. In order to solve the problem, zeolite A (EMRZA) and zeolite X (EMRZX) were synthesized by EMR. The pure phase zeolites were synthesized by alkaline melting and hydrothermal two-step process, which had high crystallinity and excellent crystal control. And the optimum conditions for synthesis of zeolite were investigated: NaOH-EMR mass ratio = 1.2, L/S = 10, hydrothermal temperature = 90 °C, and hydrothermal time = 6 h. Then, EMRZA and EMRZX showed excellent adsorption of Cd2+. When T = 25 °C, time = 120 min, pH = 6, C0 = 518 mg·L−1, and quantity of absorbent = 1.5 g·L−1, the adsorption capacities of EMRZA and EMRZX reached 314.2 and 289.5 mg·g−1, respectively. In addition, after three repeated adsorption–desorption cycles, EMRZA and EMRZX retained 80% and 74% of the initial zeolites removal rates, respectively. Moreover, adsorption results followed quasi-second-order kinetics and monolayer adsorption, which was regulated by a combination of chemisorption and intra-particle diffusion mechanisms. The adsorption mechanism was ions exchange between Cd2+ and Na+. In summary, it has been confirmed that EMRZA and EMRZX can be reused as highly efficient adsorbents to treat Cd2+-contaminated wastewater.

Anthropogenic, Carbon-Reinforced Soil as a Living Engineered Material.

In recent years, the simple synthesis of artificial humic substances (A-HS) by alkaline hydrothermal processing of waste biomass was described. This A-HS was shown to support water and mineral binding, to change soil structure, to avoid fertilizer mineralization, and to support plant growth. Many of the observed macroscopic effects could, however, not be directly related to the minute amounts of A-HS which have been added, and an A-HS stimulated microbiome was found to be the key for understanding. In this review, we describe such anthropogenic soil in the language of the modern concept of living engineered materials and identify natural and artificial HS as the enabler to set up the interactive microbial system along the interfaces of the mineral grains. In that, old chemical concepts as surface activity, redox mediation, and pH buffering are the base of the system structure build-up and the complex self-adaptability of biological systems. The resulting chemical/biological hybrid system has the potential to address world problems as soil fertility, nutrition of a growing world population, and climate change.

Extraction of Novel Effective Nanocomposite Photocatalyst from Corn Stalk for Water Photo Splitting under Visible Light Radiation

Novel (Ca, Mg)CO3&SiO2 NPs-decorated multilayer graphene sheets could be successfully prepared from corn stalk pith using a simple alkaline hydrothermal treatment process followed by calcination in an inert atmosphere. The produced nanocomposite was characterized by SEM, EDX, TEM, FTIR, and XRD analytical techniques, which confirm the formation of multilayer graphene sheets decorated by inorganic nanoparticles. The nanocomposite shows efficient activity as a photocatalyst for water-splitting reactions under visible light. The influence of preparation parameter variations, including the alkaline solution concentration, hydrothermal temperature, reaction time, and calcination temperature, on the hydrogen evolution rate was investigated by preparing many samples at different conditions. The experimental work indicated that treatment of the corn stalk pith hydrothermally by 1.0 M KOH solution at 170 °C for 3 h and calcinating the obtained solid at 600 °C results in the maximum hydrogen production rate. A value of 43.35 mmol H2/gcat.min has been obtained associated with the energy-to-hydrogen conversion efficiency of 9%. Overall, this study opens a new avenue for extracting valuable nanocatalysts from biomass wastes to be exploited in hot applications such as hydrogen generation from water photo-splitting under visible light radiation.

Ho2O3-TiO2 Nanobelts Electrode for Highly Selective and Sensitive Detection of Cancer miRNAs.

The design and engineering of effective electrode materials is critical in the development of electrochemical sensors. In the present study, Ho2O3-TiO2 nanobelts were synthesized by an alkaline hydrothermal process. The structure and morphology were investigated by X-ray diffraction (XRD) and field emission scanning electron microscope (FESEM) measurements. The Ho2O3-TiO2 nanobelts showed a distinctly enhanced (004) reflection peak and rough surfaces and were used for the electrochemical selective sensing of various cancer miRNAs, such as prostate cancer miR-141, osteosarcoma miR-21, and pancreatic cancer miR-1290. Voltammetric measurements showed an oxidation peak at +0.4, +0.2, and +1.53 V for the three different cancer biomarkers, respectively, with the detection limit as low as 4.26 aM. The results suggest that the Ho2O3-TiO2 nanobelts can be used as active materials to detect early cancers, for in vitro screening of anticancer drugs, and molecular biology research.

Preparation of TiO2 nanofibers, porous nanotubes, RGO/TiO2 composite by electrospinning and hydrothermal synthesis and their applications in improving the electrochemical hydrogen storage properties of Co2B material

Co2B hydrogen storage material was prepared via a high temperature solid phase process. The TiO2 nanofibers (TiO2–NF) and TiO2 porous nanotubes (TiO2-NT) with different size, structure and morphology were fabricated by electrospinning and hydrothermal synthesis. In order to improve the conductivity, the reduced graphene oxide/TiO2 nanotubes composite (RGO/TiO2-NT) was synthesized by an alkaline hydrothermal process. The three-dimensional porous TiO2 nanotubes were attached to the two-dimensional RGO and formed a uniform dispersion. For the purpose of improving the electrochemical performance of Co2B, composites of Co2B doped with TiO2–NF, TiO2-NT and RGO/TiO2-NT were manufactured by ball milling. Ultimately, all the composite electrodes showed higher discharge capacities than ordinary Co2B. Among them, Co2B modified with RGO/TiO2-NT exhibited the highest discharge capacity (691.4 mAh/g). TiO2-NT with large specific surface area and unique tubular porous structure can offer sufficient electrochemical active sites to anchor hydrogen and improve the electrocatalytic activity of Co2B, meanwhile, the RGO component in RGO/TiO2-NT with excellent electrical conduction can further provide fast channels for charger transfer during the charging/discharging processes. Moreover, the corrosion resistance, HRD and kinetics performance of Co2B were also enhanced after doping of TiO2–NF, TiO2-NT and RGO/TiO2-NT.

Facile, fluorine-free fabrication of bacterial antifouling titanium alloy Ti6Al4V surfaces for surgically implanted devices

The demand for hip arthroplasties and other joint replacement orthopedic surgeries is on the rise. Combined with the emergence of antibiotic drug resistant strains of pathogenic bacteria, there is an increasing need for the development of bacterial antifouling surface treatment technologies which can be applied to titanium alloy medical devices. Herein is reported the development of a durable, fluorine-free superhydrophobic surface treatment for Ti6Al4V, fabricated through facile means without the use of HF or fluoropolymers, utilizing safe reagents under mild reaction conditions. Nanoscale texturing was created with an alkaline hydrothermal process. An alkyl surface chemistry was imparted via the deposition of an alkyl self-assembled monolayer to achieve superhydrophobic, non-wetting behavior. This superhydrophobic surface is capable of imposing 1.55 ± 0.13 and 1.72 ± 0.23 log10 reductions in the adherent populations of Gram-positive Staphylococcus aureus (S. aureus) and Gram-negative Pseudomonas aeruginosa (P. aeruginosa) bacteria, respectively. This represents a safe route to a significant potential mitigation in the costs and dangers arising from medical device associated infections.

The Extraction of Silica from Nickel Laterite Ore by Alkaline Hydrothermal Process

The Extraction of Silica from Nickel Laterite Ore by Alkaline Hydrothermal Process

Production of artificial humic acid from biomass residues by a non-catalytic hydrothermal process

Humic substance is vital for soil fertility and has wide applications such as soil remediation agents, organic fertilizer and adsorbents. The results of pH effect on artificial humic acids (AHAs) production demonstrated that acid hydrothermal conditions are favorable for biomass waste dissolution and formation of AHA precursors such as saccharides, furans, organic acids and phenols; whereas alkaline hydrothermal conditions are suitable for AHAs production from these precursors. Enhanced humification from biomass waste with a combined acid - alkaline hydrothermal process was proposed. The solid product known as hydrochar was reduced to only 5 wt% after this process indicating the significant improvement of dissolution and transformation. The AHAs concentration of 28.28 ± 0.98 wt% obtained from corn stalk was the highest yield so far, 10 times higher than ever reported. The carbon flow analysis indicated that the selectivity of AHA-C was 43.2% of the initial carbon in corn stalk. Our study provides a new way of mass production of AHAs in short period, which has great potential for industry application.

One-Step Preparation of Nitrogen-Doped Graphene Quantum Dots With Anodic Electrochemiluminescence for Sensitive Detection of Hydrogen Peroxide and Glucose.

Simple and efficient synthesis of graphene quantum dots (GQDs) with anodic electrochemiluminescence (ECL) remains a great challenge. Herein, we present an anodic ECL-sensing platform based on nitrogen-doped GQDs (N-GQDs), which enables sensitive detection of hydrogen peroxide (H2O2) and glucose. N-GQDs are easily prepared using one-step molecular fusion between carbon precursor and a dopant in an alkaline hydrothermal process. The synthesis is simple, green, and has high production yield. The as-prepared N-GQDs exhibit a single graphene-layered structure, uniform size, and good crystalline. In the presence of H2O2, N-GQDs possess high anodic ECL activity owing to the functional hydrazide groups. With N-GQDs being ECL probes, sensitive detection of H2O2 in the range of 0.3–100.0 μM with a limit of detection or LOD of 63 nM is achieved. As the oxidation of glucose catalyzed by glucose oxidase (GOx) produces H2O2, sensitive detection of glucose is also realized in the range of 0.7–90.0 μM (LOD of 96 nM).

Structural Characterization and Antibacterial Activity of Antibiotic Streptomycin Immobilized on Zeolite Synthesized from Natural Kaolinite

This study evaluated the efficacy of antibacterial activities for a zeolite A (ZEO) sample loaded with streptomycin (STR). The ZEO was synthesized from kaolinite (KAO) via the alkaline hydrothermal process and verified with various techniques, such as X-ray Diffraction, Fourier-Transform Infrared spectroscopy, Field Emission Scanning Electron Microscopy with Energy Dispersive X-ray, Transmission Electron Microscopy, and dispersion behavior to confirm the production of ZEO with high purity and reproducibility. The cubic framework of ZEO was maintained after the immobilization of STR, indicating STR molecules' adsorption on the ZEO surface. The STR-loaded ZEO (ZS) samples were prepared in three STR concentrations (50, 100, and 200 mg/L). The samples' antibacterial activity was determined using the disc diffusion technique and minimum inhibition concentration against Gram-negative bacteria (Escherichia coli ATCC 11229) and Gram-positive bacteria (Staphylococcus aureus ATCC 6538). Both bacteria were susceptible to ZS, which showed an antibacterial effect directly proportional to the STR concentration. Thus, the synthesized ZEO synthesized from natural KAO had a good prospect as a carrier system for STR for generating a broad spectrum of antibacterial activity.

Enhanced adsorption property of TiO2 based nanoribbons produced by alkaline hydrothermal process

TiO2 is a semiconductor material with endless potential for the development of renewable energy as well as in the environmental field application. With various methods, TiO2 nanostructures with various morphology, properties and application can be developed. In this paper, the synthesis of TiO2 based nanoribbons with high adsorption property produced by alkaline hydrothermal methods were investigated. Its morphology, crystal structure and physical properties were characterized using Scanning Electron Microscope (SEM), X-ray diffraction (XRD), Fourier-transform infrared (FTIR) and Brunauer-Emmett-Teller (BET) surface area analysis. The result shows that by controlling the hydrothermal processing time, different morphology and structures of TiO2 nanoribbons with different adsorption properties can be obtained. The nanoribbons produced via alkaline hydrothermal method has width 200-300 nm and length up to several microns. It also possesses fair adsorption capacity over dyes (Rhodamine B and Methyl orange) considering its large surface area and high pore volume.

Effective Utilization of Coal Processing Waste: Separation of Low Ash Clean Coal from Washery Rejects by Hydrothermal Treatment

ABSTRACT Handling and disposal of high volume of fine coal tailings is a biggest challenge for coal washeries. Separation of clean coal by density separation and flotation shows limited yields of 23–28% and 13–14% respectively. Chemical leaching process has a challenge with the formation of insoluble salts. The present investigation aimed to separate clean coal by a combination of chemical-physical separation technique, i.e. alkaline hydrothermal process followed by density separation. Hydrothermal extraction of humic substance causes dissociation of coal aggregated structure (Mineral-Maceral-Pore structure), thus improves the separation. Experiments performed as per design of experiments and reduced design of experiments, where 100 µ particle size, 50% (w/w) pulp density, 4.5% KOH (w/w), and 140°C reaction temperature found to be optimum, at which 16.2% ash clean coal at 40.7% yield and humic acid by-product at 18.3% yield were obtained. Use of swelling agent such as tetrahydrofuran shown negative impact on clean coal recovery. Material balance and cost data were presented to show the techno-commercial viability of this technology.

The influence of crystal modifiers on the crystallinity, particle morphology and brightness of precipitated calcite powders hydrothermally prepared from black marble waste

Calcite powders were prepared from black marble waste by milling and alkaline hydrothermal processes. Crystal modifiers including two sulfates and an organophosphate chelator were used to study their effects on the crystallinity and particle morphology of calcite powders. Compared with control experiments without crystal modifiers, the Na2SO4 modifier drastically decreased the crystallinity of calcite powder, while the organophosphate modifier distinctly decreased the brightness and crystallite size of the calcite powder. Besides the rhombohedral crystallites, the calcite powders with sulfate modifiers contained a few flocculent agglomerates and nanosheets, which were assigned to amorphous/vaterite phases and portlandite phase, respectively. The organophosphate modifier induced spherical nanocrystals instead of the rhombohedral crystallites. With hydrothermal treatment performed for 4 h at 240 °C, nanosized calcite powder (88.3 nm) with a powder brightness of 94.3% was achieved at 1% organophosphate modifier. The eco-friendly technique enables the scalable recycling of marble wastes into nanosized calcite powders.

Hydrothermal processing, characterization and leaching toxicity of Cr-added “fly ash-metakaolin” based geopolymer

The detoxification and disposal of hexavalent chromium [Cr(VI)] is of real importance to the ecological environment protection and human being health. In this paper, Cr(VI) was in advance reduced to trivalent chromium [Cr3+] by Fe2+ and was immediately immobilized in a “fly ash-metakaolin” based (FMB) geopolymer through alkaline activation and hydrothermal processing. The phase structure and microstructure of the as-prepared detoxified Cr-added FMB geopolymer were investigated by XRD, FT-IR and SEM. The compressive strength and Cr(VI) leaching toxicity of the samples were also systematically investigated. The results showed that the phase compositions of the samples were mainly composed of amorphous phase, several weak crystalline phases of quartz, gismondite and sodium chloride after hydrothermal processing. The detoxified Cr can be fixed as the form of chemical bonding in the skeleton structure of FMB geopolymer. In addition, the compressive strength test results revealed that the compressive strength was mainly affected by the contents of Cr addition and reducing agent. Importantly, the extremely low leaching concentration of Cr(VI) suggested that the Cr-added FMB geopolymer prepared by hydrothermal processing possessed excellent Cr(VI) leaching toxicity, and the reduced Cr3+ was difficultly reoxidized to Cr(VI) after being immobilized in the FMB geopolymer.

Synthesis and Characterization of Arsenic(III) Oxide Nanoparticles as Potent Inhibitors of MCF 7 Cell Proliferation through Proapoptotic Mechanism

Recent advances in the nanosciences have revolutionized the diagnosis and treatment of diseases like cancers. Arsenic(III) trioxide, best known as a toxic agent, is routinely used in treating different types of leukemia. Besides its application as a chemotherapeutic drug for treating acute promyelocytic leukemia, several attempts have been made to use arsenic trioxide (ATO) against solid tumors. This is however, restricted because of the rapid renal clearance and dose-associated side effects of ATO. This work aims to address these limitations of ATO in chemotherapy by synthesizing biocompatible human serum albumin coated arsenic trioxide nanoparticles (HSA-ATONPs) by an alkaline hydrothermal process, taking sodium arsenate as a precursor. Compared with bulk ATO, these are found to have better cytotoxicity as indicated by an in vitro study with the cancer cell line MCF7. As envisaged by transmission electron microscopy, canonical signs of apoptosis were observed in the MCF 7 cells treated with HSA-ATONPs, confirmed by Annexin V-FITC staining. The study thus, reports an augmentation of the chemotherapeutic potential of arsenic trioxide in its nanoparticulate form with its surface functionalization of human serum albumin.

Peptide mass mapping in bioapatites isolated from animal bones.

Bioapatite ceramics produced from biogenic sources provide highly attractive materials for the preparation of artificial replacements since such materials are not only more easily accepted by living organisms, but bioapatite isolated from biowaste such as xenogeneous bones also provides a low-cost material. Nevertheless, the presence of organic compounds in the bioapatite may lead to a deterioration in its quality and may trigger an undesirable immune response. Therefore, procedures which ensure the elimination of organic compounds through bioapatite isolation are being subjected to intense investigation and the presence of remaining organic impurities is being determined through the application of various methods. Since current conclusions concerning the conditions suitable for the elimination of organic compounds remain ambiguous, we used the mass spectrometry-based proteomic approach in order to determine the presence of proteins or peptides in bioapatite samples treated under the most frequently employed conditions, i.e., the alkaline hydrothermal process and calcination at 500 °C. Since we also investigated the presence of proteins or peptides in treated bioapatite particles of differing sizes, we discovered that both calcination and the size of the bioapatite particles constitute the main factors influencing the presence of proteins or peptides in bioapatite. In fact, while intact proteins were detected even in calcinated bioapatite consisting of particles >250 µm, no proteins were detected in the same material consisting of particles <40 µm. Therefore, we recommend the use of powdered bioapatite for the preparation of artificial replacements since it is more effectively purified than apatite in the form of blocks. In addition, we observed that while alkaline hydrothermal treatment leads to the non-specific cleavage of proteins, it does not ensure the full degradation thereof.

Sorption capacity of seaweed-like sodium titanate mats for Co2+ removal.

The development of new technologies for securing and recycling water resources are in high demand. A key focus of these technologies is the development of various ion exchangers or adsorbents that are used for the purification of aqueous solutions. Layered sodium titanate is one of the cation exchangers utilised in the removal of heavy metals and radionuclides from wastewater. To enhance the removal efficiency, the precise design of the crystal morphology, structure, and chemical composition is important. Herein, we synthesised a unique seaweed-like sodium titanate mat (SST) using a template-free alkaline hydrothermal process. The Co2+ sorption capacity of SST was investigated by batch testing with cobalt(ii) nitrate. SST, which was synthesised from titanium sulphate in a 10 M NaOH solution at 200 °C, had a seaweed-like structure composed of randomly distributed nanofibres of layered sodium titanate that is approximately 9 nm in diameter. The crystal shape changed from roundish crystals to fibrous crystals as the hydrothermal reaction period increased. The Co2+ sorption isotherm of SST was fitted with the Langmuir isotherm model and the maximum sorption density was 1.85 mmol g−1. The selectivity of the Co2+ sorption on SST was high in comparison to that of Ca2+ and Mg2+. Herein, the Co2+ sorption mechanisms of SST were studied in comparison with commercially available sodium titanate. Results show that controlling the crystal morphology, structure, and Na concentration of the layered titanate that can be ion-exchanged determines the cation sorption properties of sodium titanate.

Synthesis of Ag‐modified TiO2 nanotube and its application in photocatalytic degradation of dyes and elemental mercury

AbstractBACKGROUNDThe non‐modified titanium dioxide (TiO2) nanotube (TNT) and silver (Ag)‐modified TNT samples were fabricated via an alkaline hydrothermal process. The synthesized samples had a high Brunauer–Emmett–Teller surface area since the resulted TNT was free of calcination, which is different from the traditional synthesized method. The specific surface area of non‐modified TNT and Ag‐modified TNT samples were 392 and 330 m2 g−1, respectively.RESULTSThe results indicated that anatase phase, cubic silver chloride (AgCl) and Ag co‐existed in the Ag‐modified TNT sample. In contrast, non‐modified TNT sample has only anatase phase. The OH groups, pre‐adsorbed water, and oxygen vacancies can be found on the surface of all samples. The Ag‐modified TNT sample showed to have higher removal efficiencies than that of non‐modified TNT sample for gas‐phase elemental mercury, carcinogenic malachite green, crystal violet and mixtures of dyes.CONCLUSIONAlthough specific surface area of non‐modified TNT was larger than that of Ag‐modified TNT, the Ag‐modified TNT possessed a high‐performance photocatalyst due to the electron‐hole pairs separation efficiency increase. © 2019 Society of Chemical Industry