Optically Active Oxygen Defects in Titanium Dioxide Doped with Inorganic Acid Ions.

Doping inorganic acid ions represents a promising pathway to improving the photocatalytic activity of TiO2, and oxygen vacancy has been regarded as the determinant factor for photocatalytic activity. A series of samples doped with Cl-, NO3-, and SO42- was prepared via a simple sol-gel method. Two different oxygen vacancies in the crystal layer of NO3-/TiO2 and Cl-/TiO2 were found, and those are [Ti3+]-V0-[Ti3+] and [Ti3+]-Cl, respectively. The photocurrent of NO3-/TiO2 with [Ti3+]-V0-[Ti3+] is significantly greater than that of Cl-/TiO2 with [Ti3+]-Cl. The least oxygen vacancy is in the gel layer of SO42-/TiO2, and the negligible photocurrent is due to difficulty in forming a stable sol. Furthermore, the process conditions for the application of TiO2 were investigated in this work. The optimal process parameters are to adjust the solution to pH = 3 during sol-gel preparation, to adopt 550 °C as the calcination temperature, and to use an alkaline electrolyte, while the rest of the preparation conditions remain unchanged. This work reveals a new avenue for designing efficient photocatalysts for air pollutant degradation.

Facile Synthesis Strategy from Sludge-Derived Extracellular Polymeric Substances to Nitrogen-Doped Graphene Oxide-Like Material and Quantum Dots.

Extracellular polymeric substances (EPS) are microbial aggregates derived from waste sewage sludge accumulated in sewage treatment plants, which provides natural, renewable, and abundant carbon, nitrogen, oxygen sources for the development of carbon materials to achieve the value-added utilization of waste sewage sludge resources. In this work, a nitrogen-doped graphene oxide (GO)-like material (N-GO) was simply produced using EPS as starting materials. A facile H2O2 oxidation-assisted method (room temperature) was developed to synthesize nitrogen-doped GO-like quantum dots (N-GOQDs) with strong tunable fluorescence from N-GO for the first time. This approach eliminates the conventional use of toxic chemicals, concentrated acids as well as expensive equipment, and strict condition requirements, which provides new insights into the synthesis of N-GO and N-GOQDs. In addition, this H2O2-assisted method was further demonstrated to prepare yellow fluorescent GO quantum dots (GOQDs) from GO successfully. The as-prepared N-GO shows excellent adsorption capacity for removing organic matters (malachite green, rhodamine B, and methylene blue) from water in 10 min. The water-soluble N-GOQDs were demonstrated to be a low toxicity and good biocompatibility fluorescence probe for bioimaging.

Microbial biomanufacture of metal/metallic nanomaterials and metabolic engineering: design strategies, fundamental mechanisms, and future opportunities.

Biomanufacturing metal/metallic nanomaterials with ordered micro/nanostructures and controllable functions is of great importance in both fundamental studies and practical applications due to their low toxicity, lower pollution production, and energy conservation. Microorganisms, as efficient biofactories, have a significant ability to biomineralize and bioreduce metal ions that can be obtained as nanocrystals of varying morphologies and sizes. The development of nanoparticle biosynthesis maximizes the safety and sustainability of the nanoparticle preparation. Significant efforts and progress have been made to develop new green and environmentally friendly methods for biocompatible metal/metallic nanomaterials. In this review, we mainly focus on the microbial biomanufacture of different metal/metallic nanomaterials due to their unique advantages of wide availability, environmental acceptability, low cost, and circular sustainability. Specifically, we summarize recent and important advances in the synthesis strategies and mechanisms for different types of metal/metallic nanomaterials using different microorganisms. Finally, we highlight the current challenges and future research directions in this growing multidisciplinary field of biomaterials science, nanoscience, and nanobiotechnology.

Dissolution magnitude and kinetics of ZnO nanoparticles mediated by water are dependent on O vacancy abundance: The environmental implications.

Metal oxide nanoparticles (NPs) dissolution in water environment is an important issue with regard to their environmental behaviors. The metal ion dissolves from surface defective site, but the effect of defect abundance remains largely unknown. This study aims to reveal this effect using ZnO NPs and O vacancy as the model system. The abundance of O vacancy is modulated by using different precursors and changing calcination atmosphere and temperature. X-ray photoelectron spectroscopy characterization shows that surface O vacancy abundance is effectively modulated to be distributed in a wide range from 15.3% to 41.8%. The deviation of O/Zn mole-ratio from 1.00 is used to denote O vacancy abundance in the bulk crystal, and the deviation reaches up to 0.32. Experiments show that the kinetics and magnitude of ZnO NPs dissolution vary in H2O, which are highly dependent on O vacancy abundance. In comparison, the specific surface area and aggregation state take minor roles. Particularly, Zn2+ dissolution rate in the first hour is more linearly correlated with surface O vacancy abundance than with specific surface area. Defects and their abundances should thus be co-considered with other physicochemical properties to fully understand the dissolution behaviors of metal oxide NPs in water environment. This study is of significance in comprehensively assessing and predicting the environmental risk of metal oxide NPs.

Enhanced adsorption for the removal of antibiotics by carbon nanotubes/graphene oxide/sodium alginate triple-network nanocomposite hydrogels in aqueous solutions.

Large-scale abuse of antibiotics has led to serious environmental problems. Some conventional adsorbents such as several biopolymer gels have poor adsorption performance and inadequate mechanical properties. In this paper, carbon nanotubes (CNTs) and graphene oxide (GO), were combined with sodium alginate (SA) to improve the adsorption performance and other properties of traditional adsorbents. With the help of hydrogen peroxide and l-cysteine (L-cys), carbon nanotubes/l-cysteine@graphene oxide/sodium alginate (CNTs/L-cys@GO/SA) triple-network composite hydrogels were prepared. Compared with traditional hydrogels and the double-network hydrogels that are currently being developed, these triple-network composite hydrogels can exploit their three-dimensional structure to improve their adsorption capacity. The independent triple-network structure increases the three-dimensional space, so there are more pores and pollutant adsorption sites to achieve the high-efficient removal of ciprofloxacin. And the adsorption capacity of CNTs/L-cys@GO/SA hydrogels can reach 181 mg g-1 and 200 mg g-1 at 25 °C and 15 °C respectively in weak acidity environment. In fact, CNTs/L-cys@GO/SA hydrogels show better property at low temperature. In addition, the thermal stability, mechanical properties and swelling ability of the triple-network hydrogels have also been improved. The independent multilayer network can retain the excellent properties of the original materials and make the internal space of hydrogels larger. These multinetwork hydrogels have great potential for removing pollutants from wastewater. In addition, the CNTs/L-cys@GO/SA hydrogels show the higher adsorption capacity of ciprofloxacin under the conditions of weak acidity, low temperature and low inorganic salt concentration, so the removal of ciprofloxacin by hydrogels can also be promoted by changing environmental conditions.

High-temperature annealing of ZnO nanoparticles increases the dissolution magnitude and rate in water by altering O vacancy distribution.

The effects and mechanism of high-temperature annealing, a frequently-used strategy to modulate the properties of nanoparticles (NPs), on the dissolution of zinc oxide (ZnO) NPs are investigated in this study. The results show that annealing increases the ZnO NPs dissolution magnitude via increasing O vacancy abundance on the surface and in the bulk crystal. The face-dependent distribution of O vacancy is revealed by characterizing ZnO single crystal, and the (000-1) face has a higher abundance than the (10-10) face. Particularly, O vacancy abundance in the bulk (000-1) is about 3 times higher than in the bulk (10-10). Annealing further strengthens the face-dependence of O vacancy distribution, therefore both raw and annealed (000-1) faces contribute dominantly to the dissolution of ZnO NPs. Typical topographies of the surface defect sites on the (000-1) face and their evolutions during dissolution are collected. Annealing promotes the formation of larger and deeper etching pits. Elevated solution temperature and annealing synergize to further accelerate ZnO dissolution. The dissolution behaviors of ZnO NPs with different annealing statuses, surface properties, and solution temperatures investigated in this study have potential implications to the evaluations of environmental fate and risk of metal oxide NPs.

Na3V2(PO4)3@C as Faradaic Electrodes in Capacitive Deionization for High-Performance Desalination.

Among various desalination technologies, capacitive deionization (CDI) has rapidly developed because of its low energy consumption and environmental compatibility, among other factors. Traditional CDI stores ions within the electric double layers (EDLs) in the nanopores of the carbon electrode, but carbon anode oxidation, the co-ion expulsion effect, and a low salt adsorption capacity (SAC) block its further application. Herein, the Faradaic-based electrode is proposed to overcome the above limitations, offering an ultrahigh adsorption capacity and a rapid removal rate. In this paper, the open framework structure Na3V2(PO4)3@C is applied for the first time as a novel Faradaic electrode in the hybrid capacitive deionization (HCDI) system. During the adsorption and desorption process, sodium ions are intercalated/deintercalated through the crystal structure of Na3V2(PO4)3@C while chloride ions are physically trapped or released by the AC electrode. Different concentrations of feedwater are investigated, and a high SAC of 137.20 mg NaCl g-1 NVP@C and low energy consumption of 2.157 kg-NaCl kWh-1 are observed at a constant voltage of 1.0 V, a concentration of 100 mM, and a flow rate of 15 mL min-1. The outstanding performance of the Na3V2(PO4)3@C Faradaic electrode demonstrates that it is a promising material for desalination and that HCDI offers great future potential.

Defects and their behaviors in mineral dissolution under water environment: A review.

Mineral dissolution is a spontaneous process that takes indispensible role in the determination of water quality in a specific water body. Deep insights into defects as a result of characterization technique development have greatly improved our understanding of their significances and behaviors in the dissolution within the mineral-water interface. Based on the progresses from previous decades, this review attempts to re-elaborate the molecular-scale process of dissolution. Material flow within the mineral/water interface is updated, with emphasis on the function of defect sites. A brief introduction of defect properties is presented, including the microscopic appearances and typical physicochemical characteristics. Feasible strategies that have been adopted to increase the defect abundance are inferred, which maybe enlightening for hydrometallurgy. The merits and drawbacks of the techniques that could be employed for the qualitative and quantitative determination of defect presence are introduced, although relatively satisfactory performances are noted. With the aid of these techniques, it is concluded that screw dislocation is the main defect type responsible for surface topography evolution as a result of dissolution. Finally, this review identifies the current knowledge gaps and future research needs for comprehensively identifying the significance of defects in mineral dissolution.

Synergistic effect between ultrasound and fierce mechanical activation towards mineral extraction: A case study of ZnO ore.

Though the positive role of ultrasound has been confirmed in the mineral extraction, its potential towards fiercely mechanically-activated mineral was not yet mentioned. In this study, as a novel mechanical activation style, bead milling (BM) was presented and ZnO ore was selected to determine its effectiveness. Results showed that median particle size of ZnO ore could be pulverized to as low as 1/164 of its original value (from ∼29.2 µm to ∼178 nm), indicating much higher activation potential of BM than that of conventional ball milling. Besides, structure destruction, even phase transformation with the direct participation of airborne CO2 occurred. All these processes rendered the superior activation capacity of BM. In view of the extraction promotion, the combination of ultrasound and BM exerted more pronounced effect than those of individual ones, indicating the synergistic effect between extra energy input (by ultrasound) and inner energy storage (by fierce BM). The classic shrinking core model with the product layer diffusion as the rate-controlling step was found to well model the extraction kinetics. The modeling disclosed high capability of ultrasound and BM combination in decreasing the activation energy (Ea) (from 54.6 kJ/mol to 26.4 kJ/mol), while ultrasound, BM could only decrease the Ea to 44.9 kJ/mol, 41.5 kJ/mol, respectively. The dual roles of ultrasound were specially highlighted: (i) participation in the extraction process via direct energy input, (ii) regulation of the aggregation that the activated ore suspension was confronted with.

A Comparison of graphene hydrogels modified with single-walled/multi-walled carbon nanotubes as electrode materials for capacitive deionization.

Capacitive deionization (CDI) is a technology used to remove salt from brackish water, and it is an energy-saving, low-cost method compared with other methods, such as reverse osmosis, multi-stage ash distillation and electrodialysis. In this paper, three-dimensional (3D) graphene hydrogels modified with single-walled carbon nanotubes (SWCNTs) or multi-walled carbon nanotubes (MWCNTs) were synthesized by a one-step water bath method to increase the conductivity of materials and reduce the aggregation of the graphene sheets. The CDI performance differences between the two materials were compared and discussed. The results suggested that SWCNTs/rGO had a higher electrosorption capacity (48.73 mg/g) than MWCNTs/rGO, and this was attributed to its high specific surface area (308.37 m2/g), specific capacity (36.35 F/g), and smaller charge transfer resistance compared with those of the MWCNTs/rGO electrode. The results indicate SWCNTs/rGO is a promising and suitable material for CDI technology and we provide basic guidance for further CNTs/graphene composite research.

Analytical and mineralogical study of a Ghana manganese ore: Quantification of Mn speciation and effect of mechanical activation.

In-depth understanding of the manganese ore would be beneficial to make the best use more environmental-friendly. A Ghana manganese ore before/after mechanical activation (MA) was therefore extensively characterized in our investigation. Surface Mn(4+)(35.5%), Mn(3+)(35.9%), Mn(2+)(28.6%) were detected by XPS, though XRD only revealed the presence of Mn(2+)-containing minerals. Thermal decomposition curve of manganese ore obtained by TG-DSC was divided into four stages from 373.15 K to 1273.15 K, which were quite consistent with the pattern of generated gases obtained by TG-FTIR and the theoretical thermodynamics analysis of the incorporated components involving ΔGT(θ) and Kp(θ). Mn species distribution showed no difference for manganese ores before/after MA, but quantitative analysis showed the decrease of residual Mn content (cannot be extracted effectively by acid, from about 12% to 1%), and thereby the increased contents of other four Mn species (exchangeables, carbonates, oxides, organics), which was suggested to be correlated with the dissociation of Mn-containing flocs and SiO2 particles witnessed by SEM-EDS. It was also found that MA could obviously promote the Mn dissolution kinetics in acid condition, though the dissolution of manganese ore before/after MA were both diffusion controlled. This investigation gives benignant inspiration for the resource utilization of manganese ore, taking the increasingly severer situation of Mn resource supply into consideration.

Oxidation of unsaturated carboxylic acids under hydrothermal conditions.

Hydrothermal oxidation pathways of high molecular weight unsaturated carboxylic acids were investigated for the potential use of chemoselectivity to improve the efficiency of the desired products from biomasses directly containing or easily producing unsaturated carboxylic acids. Hock cleavage, which frequently occur at general chemical, was observed in the absence of any acid catalyst and may be a potential major oxidation cleavage mechanism, which leads to the cleavage at both the carbon-carbon double bond and the single bond near a double bond. The addition of a peroxyl radical to the double bond may be also a potential major oxidation mechanism, which leads to the oxidation cleavage mainly at the carbon-carbon double bond. Cleavage at the carbon-carbon bond near the double bond by the addition of a peroxyl radical to the double bond may also occur. However, oxidation at either alpha-, beta-, or gamma-carbon to the -COOH group hardly occurred. These results may help to selectively produce desired products from biomasses, such as lignin and oils.