Alkali Hydrothermal Treatment Research Articles

Orthorhombic Polar Phase in Sodium Niobate Nanoribbons.

Ferroelectric materials exhibit switchable spontaneous polarization below Curie's temperature, driven by octahedral distortions and rotations, as well as ionic displacements. The ability to manipulate polarization coupled with persistent remanence, drives diverse applications, including piezoelectric devices. In the last two decades, nanoscale exploration has unveiled unique material properties influenced by morphology, including the capability to manipulate polarization, patterns, and domains. This paper focuses on the characterization of nanometric sodium niobate (SN) synthesized from metallic niobium through alkali hydrothermal treatment, utilizing electron microscopy techniques, including high-resolution differential phase contrast (DPC) in scanning transmission electron microscopy (STEM). The material exhibits a nanoribbon structure forming a tree root-like network. The study identifies crystallographic phase, atomic columns displacement directions, and surface features, such as exposed planes and the absence of particular atomic columns. The high sensitivity of integrated DPC images proves crucial in overcoming observational challenges in other STEM modes. These observations are essential for potential applications in electronic, photocatalytic, and chemical reaction contexts.

Stoichiometric Study on Ion Composition of a Precursor in Chemical Bottom-Up Synthesis for Peroxo-Titanate.

Layered alkali titanates of the lepidocrocite type are gaining enormous interest in various fields owing to their unique properties. These materials are mainly synthesized through a hydrothermal alkali treatment. However, this method uses a highly concentrated alkali solution, which has high environmental impacts and is therefore unsuitable for mass synthesis. Herein, we propose an efficient method for the large-scale synthesis of layered sodium titanate structures (Na2-x H x Ti2O5) using a recently reported bottom-up chemical process. The effects of the Na:Ti molar ratio in the peroxo-titanium complex ion precursor on the products are investigated through stoichiometric calculations for a molar ratio range of 10:1-1:1. The optimal ratio for the complete ionization of TiH2 (which is the starting material) to form the peroxo-titanium complex ion is found to be 1.1:1. The amount of alkali raw material required is 99.6% lower than that required in the traditional hydrothermal method. The crystal structures and morphologies of the samples are almost identical regardless of the Na:Ti molar ratio. The precursor-derived peroxo bonds narrow the energy band gaps of the layered titanates even when the amount of titanium ions dissolved in the precursor increases. The proposed method is not only an efficient synthetic route for mass production but also has potential applications in the development of photofunctional materials.

Inhibitory effect of microplastics derived organic matters on humification reaction of organics in sewage sludge under alkali-hydrothermal treatment

Alkali-hydrothermal treatment (AHT) of sewage sludge is often used to recover value-added dissolved organic matters (DOM) enriched with artificial humic acids (HA). Microplastics (MPs), as emerging contaminants in sewage sludge, can leach organic compounds (MP-DOM) during AHT, which potentially impact the characteristics of thermally treated sludge's DOM. This study employed spectroscopy and Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR-MS) to explore the impacts of MPs on DOM composition and transformation during AHT. The biological effects of DOM were also investigated by hydroponic experiments. The results showed that the leaching of MP-DOM led to a substantial increase in DOC content of DOM of thermally treated sludge. Conversely, the HA content significantly decreased in the presence of MPs, resulting in a decline of plant growth facilitation degree. FT-ICR-MS analysis revealed that the reduction in HA content was characterized by a notable decline in the abundance of O6–7 and N1–3O6–7 molecules. Reactomics results indicated that the leaching of MP-DOM inhibited the Maillard reaction but bolstered oxidation reactions. The inhibition of Maillard reaction, resulting in a decrease in crucial precursors (dicarbonyl compounds, ketoses, and deoxyglucosone), was responsible for the decrease of HA content. The primary mechanism responsible for inhibiting the Maillard reaction was the consumption of reactive amino reactants through two pathways. Firstly, the leaching of organic acids in MP-DOM caused decrease of sludge pH, leading to the protonation of amino groups. Secondly, the lipid-like compounds in MP-DOM underwent oxidation (-2H+O), producing fatty aldehydes that consumed the reactive amino reactants. These discoveries offer enhanced insights into the specific contribution of MPs to the composition, transformation, bioactivity of DOM during AHT process.

Enhanced dielectric properties of poly(vinylidene fluoride) matrix nanocomposites incorporated with one–dimensional structure of titanate nanotubes

The dielectric properties of polymer nanocomposites based on a poly(vinylidene fluoride) (PVDF) matrix, filled with a one–dimensional nanostructure of titanate nanotubes (TNTs), were investigated. These studies demonstrated significant improvements in the energy storage capability of the application. The TNTs were synthesized through an alkali hydrothermal treatment method at 130 °C for 24 h, using a 10 M NaOH solution. The TNTs exhibited a large dielectric permittivity of approximately 1.2 × 104 with a low loss tangent of approximately 0.12 at 1 kHz and 25 °C. TNTs/PVDF polymer nanocomposites were studied and fabricated using liquid phase–assisted dispersion and hot–pressing methods. By introducing TNTs into the PVDF polymer, both the dielectric permittivity and loss tangent increased. Notably, the polymer nanocomposite containing 50 wt. % TNTs exhibited a dielectric permittivity of 5.3 × 103 at 1 kHz, which is ∼530 times greater than that of pure PVDF (10.78), while the loss tangent remained at 0.572. The low–frequency dielectric permittivity increased with an increase in relative humidity from 50 to 95 % due to enhanced interfacial polarization at the surface and electrode interface. However, at frequencies greater than 1 kHz, the dielectric permittivity was independent of relative humidity. The improvement in the enhanced dielectric permittivity of polymer–based nanocomposites with incorporated TNTs was ascribed to these factors.

Pilot-scale continuous biogenic silica extraction from rice husk by one-pot alkali hydrothermal treatment and ball milling

BackgroundRice husk is the most silicon-rich renewable biomass and can be used as a raw material for producing silicon-based materials. With the increasing interest in utilizing rice husk as a renewable resource, the development of a robust silica extraction method is required. In this study, a one-pot alkali hydrothermal and ball-milling continuous silica extraction method was developed at the pilot scale.ResultsThree residence times (50, 100, and 150 min) were selected to compare the performance of the continuous extraction process depending on the residence time. The silica production was 4.09, 2.67, and 2.22 kg day−1 while the silica extraction yield was 52.8, 69.1, and 86.0% at resident times of 50, 100, and 150 min, respectively. The energy consumption for producing 1 kg of silica from rice husk was 51.6, 47.7, and 47.4 MJ kg−1 at resident times of 50, 100, and 150 min, respectively. The one-pot continuous silica extraction process was performed for 150 h to verify the stability of the process. During long-term operation, the process exhibited a constant solid content and stable silica extraction yield. The silicate solution obtained by the one-pot continuous process was successfully used to synthesize size-controlled spherical silica particles, which had a purity of 99.1 wt% and amorphous structure.ConclusionsOverall, this study presents a novel continuous silica extraction method for the efficient recovery of silica from rice husk-based biorefineries.Graphical abstract

Reconstruction and recovery of anatase TiO2 from spent selective catalytic reduction catalyst by NaOH hydrothermal method

The improper disposal of spent selective catalytic reduction (SCR) catalysts causes environmental pollution and metal resource waste. A novel process to recover anatase titanium dioxide (TiO2) from spent SCR catalysts was proposed. The process included alkali (NaOH) hydrothermal treatment, sulfuric acid washing, and calcination. Anatase TiO2 in spent SCR catalyst was reconstructed by forming Na2Ti2O4(OH)2 nanosheet during NaOH hydrothermal treatment and H2Ti2O4(OH)2 during sulfuric acid washing. Anatase TiO2 was recovered by decomposing H2Ti2O4(OH)2 during calcination. The surface pore properties of the recovered anatase TiO2 were adequately improved, and its specific surface area (SSA) and pore volume (PV) were 85 m2·g−1 and 0.40 cm3·g−1, respectively. The elements affecting catalytic abilities (arsenic and sodium) were also removed. The SCR catalyst was resynthesized using the recovered TiO2 as raw material, and its catalytic performance in NO selective reduction was comparable with that of commercial SCR catalyst. This study realized the sustainable recycling of anatase TiO2 from spent SCR catalyst.

Facile synthesis of nanofibrous and hollow titania microspheres as drug‐laden cell carriers

AbstractMicrospheres are one type of promising cell‐supporting matrices. However, the synthesis of nanofibrous and hollow microspheres as drug‐laden cell carriers is still a great challenge. Here, the nanofibrous and hollow titania nanowire (NH‐TiNW) microspheres were synthesized by in situ alkali hydrothermal treatment of hollow titania (H‐Ti) microspheres, and their microstructure, biocompatibility, and drug delivery property were evaluated. By controlling hydrothermal temperature from 80 to 120°C and hydrothermal time from 1 to 4 h, the surface of H‐Ti microspheres was controllably tailored with nanoparticles and NWs. The results showed that NH‐TiNW microspheres were spherical in morphology with a diameter of 100–200 µm, hierarchically assembled by numerous TiNWs with the diameter of 10–20 nm, and possessed a nanofibrous and hollow structure. In vitro biocompatibility evaluation showed that NH‐TiNW microspheres presented an enhanced cell attachment and proliferation compared with H‐Ti microspheres due to the presence of the nanofibrous surface. Drug delivery evaluation showed that NH‐TiNW microspheres strongly adsorbed tetracycline hydrochloride (one type of antibiotic, model drug) with a loading efficiency of 81.5% ± 1% due to the presence of the nanofibrous and hollow structure and also effectively maintained the biological efficiency of the loaded drugs to inhibit the growth of bacteria.

Biostimulants in dissolved organic matters recovered from anaerobic digestion sludge with alkali-hydrothermal treatment: Nontarget identification by ultrahigh-resolution mass spectrometry

Recovering high-value biomaterials from anaerobic digestion sludge (ADS) has attracted considerable attention. However, the molecular features and biological effects of abundant dissolved organic matters (DOMs) in ADS are still unclear, which limits the efficient recycling and application of these bioproducts. This study investigated the molecular composition and transformation of DOMs recovered from ADS through a mild-temperature alkali-hydrothermal treatment (AHT) with ultrahigh-resolution mass spectrometry and energy spectroscopy, and the fertilizing effects of DOMs were evaluated by rice hydroponics. The results indicated that AHT processes significantly promoted the solubilization and release of DOMs from ADS, where most of DOMs molecules remained unchanged and mainly consisted of N-containing compounds with 1–3 N atoms, featuring aromatic or N-heterocyclic rings. Furthermore, AHT processes at pH of 9–10 induced the hydrolysis of partial protein-like substances in DOMs, which was accompanied by formation of heterocyclic-N compounds. Under AHT at pH of 11–12, protein-like and heterocyclic-N substances were increasingly decomposed into amino-N compounds containing 1 or 5 N atoms, while numerous oxygenated aromatic substances with phytotoxicity were degraded and removed from DOMs. Rice hydroponic test verified that ADS-derived DOMs recovered by AHT process at pH of 12 exhibited the highest bioactivity for rice growth, which was attributed to the abundance of amino compounds and humic substances. This study proposed a novel process for the recovery of high-quality liquid organic fertilizer from ADS through AHT process, which can further enrich the technical options available for the safe utilization of sludge resources.

Use of activated quartz powder as an alkaline source for producing one-part Ca-rich slag based cementitious materials: Activation mechanism, strength, and hydration reaction

As one of the most typical mineral phases in the mine tailings (MTs), the reactivity of quartz has a remarkable influence on the hydration properties of MTs based cementitious materials. In this study, the pure quartz powder (QP) through the alkali-hydrothermal activation was used as an alkaline source for producing one-part Ca-rich slag based cementitious materials (OPM), and the activation mechanism of QP, compressive strength, hydration heats, hydration reactants, and microstructure of OPM samples were investigated, which contributes to evaluate the performance of MTs-based cementitious materials. The reactivity of crystalline QP was enhanced via an alkali-hydrothermal treatment at 200–300 °C in the presence of NaOH. Sodium silicate reactant in the activated QP can dissolve in water to release OH− and Si species, making it an alkaline source for the OPM preparation. Just like cement, OPM samples were synthetized by only adding water to the mixture of activated QP and Ca-rich slag. Appropriate ratios of starting materials were beneficial for the increase in hydration rate, generation of numbers of hydration products, and refinement of microstructure of OPM samples. When the weight ratio of activated QP and slag was 40:60, the OPM sample showed a 28-day strength of 47.6 MPa. Based on the Chinese GB/T 175–2007 standard, this strength development reaches the requirement of 42.5 cement and exhibits the possibility that the OPM sample may be applied in the general construction field.

Micro-meso hierarchical ZSM-5 zeolite supported RuOx nanoparticles for activity enhancement of catalytic vinyl chloride oxidation

Hierarchical ZSM-5 zeolites were synthesized by an alkali hydrothermal treatment strategy and adopted as support materials for the fabrication of RuOx nano catalysts. The physicochemical properties and catalytic activities for vinyl chloride (VC) oxidation over the resultant RuOx/HZ5-nd (n = 2, 3, 4) catalysts were successfully modulated by the treatment time regulation (2d, 3d and 4d) of ZSM-5 solid. Experimental results demonstrated that the RuOx/HZ5-nd catalysts possessed notable cavity-shell structures with micro-meso hierarchical porosity, which brought about the increased specific surface area, the enhanced low-temperature reducibility and the strengthened surface acidity comparable to RuOx/HZ5. All these superiorities were recognized as the crucial origin for boosting catalytic oxidation of VC. Especially, the RuOx@HZ5-3d catalyst exhibited the optimum VC oxidation activity with the lowest T50 and T90 (temperature at 50 and 90% conversion) of 275 and 297 °C, which was 22 and 24 °C lower than those of RuOx/HZ5. Importantly, RuOx@HZ5-3d exhibited significantly high thermal stability, water resistant and regeneration capacity from humid conditions, which made it a promising material for the catalytic purification of chlorinated volatile organic compounds.

In situ hydrothermal growth and in vitro biocompatibility of TiO2 nanowires grown on TiO2 nanoparticle compacts as novel supportive substrates

ABSTRACT In this work, TiO2 nanoparticle (NP) compacts were employed as novel supportive substrates for synthesis of TiO2 nanowires (NWs) with controlled diameter via an alkali hydrothermal route. SEM observations showed that the alkali hydrothermal treatment caused an in situ conversion of TiO2 NPs on the outer surface of the compacts to TiO2 NWs. The diameter of each individual NW could be facilely tailored from 10 nm to 500 nm through adjustment of the hydrothermal temperature and reaction time. Moreover, compared with TiO2 NWs grown on the conventional Ti metals, those grown on the compacts were much more stable in the aqueous solution. In vitro biocompatible evaluation indicates that the as-synthesised TiO2 NWs supported attachment and proliferation of fibroblasts L929 cells, indicating a good biocompatibility. Moreover, TiO2 NWs with small diameter significantly enhanced cell attachment and proliferation. Thus, the as-synthesised TiO2 NWs might have a potential as novel biocompatible tissue regenerative matrix.

Biostimulants in Dissolved Organic Matters Recovered from Anaerobic Digestion Sludge with Alkali-Hydrothermal Treatment: Nontarget Identification by Ultrahigh-Resolution Mass Spectrometry

Biostimulants in Dissolved Organic Matters Recovered from Anaerobic Digestion Sludge with Alkali-Hydrothermal Treatment: Nontarget Identification by Ultrahigh-Resolution Mass Spectrometry

Enhancement of Bone Regeneration on Calcium-Phosphate-Coated Magnesium Mesh: Using the Rat Calvarial Model.

Metallic biodegradable magnesium (Mg) is a promising material in the biomedical field owing to its excellent biocompatibility, bioabsorbability, and biomechanical characteristics. Calcium phosphates (CaPs) were coated on the surface of pure Mg through a simple alkali-hydrothermal treatment. The surface properties of CaP coatings formed on Mg were identified through wettability, direct cell seeding, and release tests since the surface properties of biomaterials can affect the reaction of the host tissue. The effect of CaP-coated Mg mesh on guided bone regeneration in rat calvaria with the critical-size defect was also evaluated in vivo using several comprehensive analyses in comparison with untreated Mg mesh. Following the application of protective CaP coating, the surface energy of Mg improved with higher hydrophilicity and cell affinity. At the same time, the CaP coating endowed Mg with higher Ca affinity and lower degradation. The Mg mesh with CaP coating had higher osteointegration and bone affinity than pristine Mg mesh.

Synthesis of hierarchical and flower-like TiO2 nanowire microspheres as biocompatible cell carriers

Fibrous materials are of great interest in the development of tissue regenerative matrix. However, synthesis of inorganic fibrous microspheres as cell carriers is a great challenge. In this study, we for the first time report on the synthesis of novel hierarchical and flower-like TiO2 nanowire (NW) microspheres as biocompatible cell carriers. TiO2 NW microspheres were synthesized through in situ alkali hydrothermal treatment of the TiO2 nanoparticle (NP) microspheres and their microstructure, formation mechanism and in vitro biocompatibility were evaluated. SEM observations show that the resulting TiO2 NW microspheres were constructed by a large number of NWs with the diameter of 10–20 nm and exhibited a flower-like and hierarchical morphology with the diameter of 400–600 μm. XRD patterns indicate that TiO2 NW microspheres were constructed by both rutile and anatase phase of TiO2. FT-IR spectra reveal that Ti-O-Ti bonds were involved in TiO2 NW microspheres. In vitro biocompatibility was evaluated by seeding the fibroblast L929 cells on the microspheres. A conventional MTT assay quantitatively indicates that the TiO2 NW microspheres favored adhesion and proliferation of cells and were biocompatible, while SEM observations qualitatively confirmed that the cells were well grown on the surface of TiO2 NW microspheres. Thus, the as-synthesized TiO2 NW microspheres would be applicable to novel and biocompatible cell carriers.

Alkali-Hydrothermal Treatment of K-Rich Igneous Rocks for Their Direct Use as Potassic Fertilizers

Due to the increasing demand for conventional sources of potassium (K) and their inaccessibility by African countries, K-rich igneous rocks are increasingly studied as potential alternative sources. In this study, six potassic igneous rocks (syenites and trachytes) from the Tamazeght, Jbel Boho, Ait Saoun, and El Glo’a regions (Morocco) were sampled and characterized. Then they were hydrothermally treated to enhance their K release for potential use as potassic fertilizers. The raw materials are mainly formed by microcline (up to 74%), orthoclase (20–68%), albite (36–57%), biotite-muscovite (15–23%), and titanite, calcite, hematite, and apatite as accessory minerals. These samples were crushed and milled to reach a particle size <150 µm and mixed with 4 N NaOH solution in an autoclave. The liquid/solid (L/S) ratio was about 44 mL/50 g. The powders were allowed to react with the solution at 170 °C for 7 h. For all tests, NaOH reacted completely with the powders and no liquid was observed after the treatment. X-ray diffraction (XRD), thermal gravimetric analysis (TGA), infrared spectroscopy (IRTF), and scanning electron microscopy (SEM-EDS) were carried out on treated samples to characterize the mineralogical and structural changes due to the alkali-hydrothermal treatment. Indeed, the treated samples revealed the presence of sodic neoformed phases such as thermonatrite, sodalite, analcime, and cancrinite. The treated material was leached for a week using deionized water and the elements released were measured using inductively coupled plasma–atomic emission spectroscopy (ICP-AES). The hydrothermal process showed a strong effect on structure breakdown as well as on the release of K and other nutrients such as P, Fe, Si, Mg, and Ca. Therefore, the alkali-hydrothermal treatment allowed the release of 50.5 wt% K. Moreover, the release of Mg, Ca, Fe, P, K, and Si were significantly increased. Mg, Ca, Fe, P, K, and Si release within raw materials was about (0.5–3.6), (3.5–31.4), (0.01–0.4), (0.01–0.3), (20–55), and (4.6–8) mg/kg, respectively, whereas treated samples showed a higher release of these elements. Quantitatively, Mg, Ca, Fe, P, K, and Si releases were about (10–11.8), (60–70), (7–20), (1.2–15), (218–1278), and (1119–2759) mg/kg, respectively. Consequently, the treated igneous rocks (syenite and trachyte) could be directly used as potassic fertilizers that would also be a source of other nutrients.

Alkali Hydrothermal Treatment to Synthesize Hydroxyl Modified g-C3N4 with Outstanding Photocatalytic Phenolic Compounds Oxidation Ability

The treatment of phenol-containing wastewater is a hot topic in the field of environmental chemistry. In this work, the hydroxyl grafted graphite phase carbon nitride (g-C3[Formula: see text] was prepared by alkaline hydrothermal (AH) treatment, and its degradation of phenol under visible light was investigated. XRD, UV-Vis, FT-IR, XPS, N2 adsorption, PL, ESR, TPD and EIS were used to characterize the as-prepared catalysts. The results showed that the hydroxyl group grafting does not influence the crystal structure, optical property and specific surface area of catalyst. Compared with the hydroxyl group modified g-C3N4 prepared by H2O2 method, the alkali hydrothermal treatment can graft more hydroxyl groups onto the g-C3N4 surface, leading to the higher electron–hole separation efficiency. The as-prepared catalyst using this method had more surface negative charges and stronger adsorption capacity for the reaction substrate phenol. The g-C3N4 prepared by this alkali hydrothermal treatment displayed the phenol degradation rate constant of 0.22[Formula: see text]h[Formula: see text], which is 3.72 and 2.06 times higher than that of neat and H2O2 treated g-C3N4, as well as excellent catalytic stability and structural stability. The possible reaction mechanism was proposed.

Effect of alkali strength on the hydrothermal growth of photoactive TiO2 nanowires

Titanium dioxide nanowires have been prepared by the alkali hydrothermal treatment of TiO2 nanoparticles in presence of different hydroxides and characterized using transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive x-ray (EDX), N2 adsorption-desorption measurements, powder x-ray diffraction (XRD) and UV-Vis spectroscopy. Interestingly, only the strong bases (NaOH and KOH) formed mainly anatase titanium dioxide nanowires with the evident collapse of definitive (110) rutile XRD peak. The KOH-based titanium oxide nanowires exhibited comparatively low diameter (∼5 nm), high surface area (228.34 m2/g), and low band gap energy (2.90 eV), and showed the most remarkable photocatalytic degradation (98.87 %). However, the NH4OH-based titanium dioxides were nanoparticles having insignificantly modified morphology and least photocatalytic efficiency. The effect of operating variables on the degradation of aqueous methylene blue (MB) over the obtained alkali hydrothermal TiO2 was studied using response surface methodology, based on a bivariate central composite design (CCD) and optimized numerically.

A sequential integration approach using Aspergillus Niger to intensify coal fly ash as a rare metal pool

As the primary solid waste product from coal-fired power plants, a large amount of coal fly ash (CFA) has caused serious environmental pollution to cultivated land, groundwater, and regional air. Meanwhile, CFA contains certain amounts of rare metals, making it a potential rare metal pool (RMP). Reducing CFA stock can alleviate its pollution to environment through an effective recycling approach. However, the extraction of rare metals from CFA, a pool of rare metals, has not received enough attention until now. Here, we present a sequential integration approach (SIA) of hydrothermal alkali treatment (HAT) and bioleaching to enhance recovery rate of rare metals from CFA. The results showed that the leaching rates of Ti, Ga, Sr, Zr, and Ba were significantly increased using one-step extraction method, reaching 89.20%, 32.00%, 54.30%, 74.50%, and 35.40%, respectively. The results demonstrated that HAT combined with bioleaching can improve the recovery rate of some rare metals from CFA. This study sheds new light on the valuable development of CFA as RMP with potential to mitigate the environment pollution.

An integrated approach combines hydrothermal chemical and biological treatment to enhance recycle of rare metals from coal fly ash

Coal fly ash rich in rare metals accounts for a large amount of solid waste released from coal-fired power plants. However, rare metals, the components of coal fly ash with the highest economic value, are not fully recycled due to the lack of an effective, low-cost approach. Therefore, it is urgent to develop a new approach, aiming at increasing the recycling efficient, decreasing the cost and strengthening the high economic value of fly ash. Here, we developed an integrated approach combines hydrothermal chemical treatment process (HTCP) and biological leaching process (BLP) to improve recycle of rare metals from coal fly ash. The results showed that the one-step bioleaching method could obtain more kinds of rare metals and dramatically improve bioleaching rate after hydrothermal-alkali treatment (HAKT) using Acidithiobacillus thiooxidans. After HAKT, the leaching rates of metals V, Sr, Y, La, and Ce were higher than those of the untreated pure fly ash (UPFA) with the maximum values of 51%, 70.52%, 37.48%, 64.77%, and 76.37%, respectively; after hydrothermal-acid treatment (HTAT), the bioleaching rates of rare metals Ni, Sr, and Y, were higher than those of the UPFA with the maximum values of 70.24%, 20.26%, and 34.54% respectively. The results also showed that, for most rare metals, the recovery rate following HAKT was higher than that following HTAT. This result can be demonstrated via analyzing adsorption quantity, adsorption kinetics and diffusion model of fly ashes for A.thiooxidans. Our study provides an important pathway for recycling rare metals from coal fly ash.

Construction of a ternary g-C3N4/TiO2@polyaniline nanocomposite for the enhanced photocatalytic activity under solar light

The combination of two or more semiconductor materials for the synthesis of new hybrid photocatalyst could be a good approach to enhance the visible light absorption, electron-hole (e−/h+) pair separation rate and photocatalytic decomposition of the organic contaminants. Herein, a facile in situ oxidative polymerization method has been used for the synthesis of visible light active g-C3N4/TiO2@polyaniline (g-C3N4/TiO2@PANI) nanocomposite for the decomposition of the congo red (CR) under the solar light irradiation. Prior to making the composite of TiO2 (P25) with g-C3N4 and polyaniline, a lamellar structure was generated onto the TiO2 brim by alkali hydrothermal treatment to enhance the surface area and adsorption properties. The PL and UV-visible analysis clearly showed the fast separation of the e−/h+ pair, and reduction in the bandgap energy of the g-C3N4/TiO2@PANI nanocomposite. The results revealed TiO2, PANI and g-C3N4 showed the synergestic behavior in the g-C3N4/TiO2@PANI nanocomposite and greatly enhanced the photocatalytic degradation of the CR. The photocatalytic decomposition of the CR was almost 100% for 20 mg/L at pH 5, 7 and 180 min. The reusability study of the spent catalyst showed the 90% degradation of CR after four consecutive cycles indicate that g-C3N4/TiO2@PANI nanocomposite is a stable and efficient catalyst. The high efficiency and reusability of the g-C3N4/TiO2@PANI nanocomposite could be attributed to the higher visible light absorption and sensitizing effect of the g-C3N4 and PANI.