In Situ Reconstructed Zn doped Fex Ni(1- x ) OOH Catalyst for Efficient and Ultrastable Oxygen Evolution Reaction at High Current Densities.

Developing FeOOH as a robust electrocatalyst for high output oxygen evolution reaction (OER) remains challenging due to its low conductivity and dissolvability in alkaline conditions. Herein, it is demonstrated that the robust and high output Zn doped NiOOH-FeOOH (Zn-Fex Ni(1-x) )OOH catalyst can be derived by electro-oxidation-induced reconstruction from the pre-electrocatalyst of Zn modified Ni metal/FeOOH film supported by nickel foam (NF). In situ Raman and ex situ characterizations elucidate that the pre-electrocatalyst undergoes dynamic reconstruction occurring on both the catalyst surface and underneath metal support during the OER process. That involves the Fe dissolution-redeposition and the merge of Zn doped FeOOH with in situ generated NiOOH from NF support and NiZn alloy nanoparticles. Benefiting from the Zn doping and the covalence interaction of FeOOH-NiOOH, the reconstructed electrode shows superior corrosion resistance, and enhanced catalytic activity as well as bonding force at the catalyst-support interface. Together with the feature of superaerophobic surface, the reconstructed electrode only requires an overpotential of 330 mV at a high-current-density of 1000 mA cm-2 and maintains 97% of its initial activity after 1000 h. This work provides an in-depth understanding of electrocatalyst reconstruction during the OER process, which facilitates the design of high-performance OER catalysts.

Construction of MoS2@Activated Alumina Beads as Catalysts for Rapid Gold Recovery from Au(S2O3)23- Solution.

Gold recovery from thiosulfate leaching solution Au(S2O3)23- is regarded as a tough task because of the low efficiency and complex procedure in current technology, which hindered the industrial application of this eco-friendly technique. In this work, a MoS2@activated alumina bead composite (MoS2@AA) was constructed through a simple hydrothermal anchoring method and served as a catalyst to recover gold from Au(S2O3)23- solution for the first time. The microstructure and chemical component of MoS2@AA were systematically analyzed. In addition, batch experiments were carried out to explore the recovery behavior of Au(S2O3)23- (concentration: 10 to 200 ppm). Ascribing to the extraordinary optical property of MoS2@AA, Au(S2O3)23- could be directly reduced to Au0 by photogenerated electrons and then form a two-phase interface of gold/MoS2@AA. As a result, the recovery of Au(S2O3)23- can reach up to 98% on MoS2@AA, which was much higher than traditional methods. More importantly, the reduced Au0 could be desorbed from MoS2@AA through a supersonic method, achieving one-step Au0 recovery from Au(S2O3)23-. This novel strategy used in this research has great significance to the development of Au(S2O3)23- recovery in the future.

Free Nitrous Acid Inhibits Atenolol Removal during the Sidestream Partial Nitritation Process through Regulating Microbial-Induced Metabolic Types.

Limited studies have attempted to evaluate pharmaceutical removal during the sidestream partial nitritation (PN) process. In this work, atenolol biodegradation by PN cultures was investigated by maintaining ammonium and pH at different levels. For the first time, free nitrous acid (FNA), other than ammonium, pH, and free ammonia, was demonstrated to inhibit atenolol removal, with biodegradation efficiencies of ∼98, ∼67, and ∼28% within 6 days at average FNA levels of 0, 0.03, and 0.19 mg-N L-1, respectively. Ammonia-oxidizing bacteria (AOB)-induced metabolism was predominant despite varying FNA concentrations. In the absence of ammonium/FNA, atenolol was mostly biodegraded via AOB-induced metabolism (65%) and heterotroph-induced metabolism (33%). AOB-induced metabolism was largely inhibited (down to 29%) at 0.03 mg-N L-1 FNA, while ∼27 and ∼11% were degraded via heterotroph-induced metabolism and AOB-induced cometabolism, respectively. Higher FNA (0.19 mg-N L-1) substantially reduced atenolol biodegradation via heterotroph-induced metabolism (4%), AOB-induced metabolism (16%), and AOB-induced cometabolism (8%). Newly identified products and pathways were related to metabolic types and FNA levels: (i) deamination and decarbonylation (AOB-induced cometabolism, 0.03 mg-N L-1 FNA); (ii) deamination from atenolol acid (heterotrophic biodegradation); and (iii) nitro-substitution (reaction with nitrite). This suggests limiting FNA to realize simultaneous nitrogen and pharmaceutical removal during the sidestream process.

Synthetic Fe-rich nontronite as a novel activator of bisulfite for the efficient removal of tetracycline.

In this work, the iron-containing smectite nontronite (NNT) was artificially prepared by hydrothermal process and used as a heterogeneous catalyst to activate bisulfite (BS) for degradation of tetracycline (TC). Two NNT samples with different iron content (NNT1 and NNT2) were characterized by XRD, FTIR, XPS and SEM-EDS analysis. Under dark condition, the TC removal rates of NNT1/BS and NNT2/BS reached about 91.7% and 95.5% respectively at 60 min. Due to the heterogeneous catalysis of structural Fe(III), the NNT catalysts showed great catalytic activity and low iron leaching at the pH range 3.0-7.5. In addition, NNT particles were also stable and reusable in activating BS for TC removal. According to the EPR and radical quenching experiments, it could be proved that the precursor radical •SO3- was first generated in NNT/BS system, then •SO4- and •OH were the active species that played a role in TC degradation. The synthetic NNT clay is a promising Fe-based catalyst for treatment of TC wastewater thanks to its high activity, good stability and effective reusability.

Cometabolic biodegradation of antibiotics by ammonia oxidizing microorganisms during wastewater treatment processes.

Studies on antibiotic removal during wastewater treatment processes are crucial since their release into the environment could bring potential threats to human health and ecosystem. Cometabolic biodegradation of antibiotics by ammonia oxidizing microorganisms (AOMs) has received special attentions due to the enhanced removal of antibiotics during nitrification processes. However, the interactions between antibiotics and AOMs are less well-elucidated. In this review, the recent research proceedings on cometabolic biodegradation of antibiotics by AOMs were summarized. Ammonia oxidizing bacteria (AOB), ammonia oxidizing archaea (AOA) and complete ammonia oxidizers (comammox) played significant roles in both nitrification and cometabolic biodegradation of antibiotics. Antibiotics at varying concentrations might pose inhibiting or stimulating effect on AOMs, influencing the microbial activity, community abundance and ammonia monooxygenase subunit A gene expression level. AOMs-induced cometabolic biodegradation products were analyzed as well as the corresponding pathways for each type of antibiotics. The effects of ammonium availability, initial antibiotic concentration, sludge retention time and temperature were assessed on the cometabolic biodegradation efficiencies of antibiotics. This work might provide further insights into the fate and removal of antibiotics during nitrification processes.

Enhanced biodegradation of ciprofloxacin by enriched nitrifying sludge: assessment of removal pathways and microbial responses.

Antibiotics are mostly collected by sewage systems, but not completely removed within wastewater treatment plants. Their release to aquatic environment poses a great threat to public health. This study evaluated the removal of a widely used fluoroquinolone antibiotic, ciprofloxacin, in enriched nitrifying culture through a series of experiments by controlling ammonium concentrations and inhibiting functional microorganisms. The removal efficiency of ciprofloxacin at an initial concentration of 50 µg L-1 reached 81.86 ± 3.21% in the presence of ammonium, while only 22.83 ± 8.22% of ciprofloxacin was removed in its absence. A positive linear correlation was found between the ammonia oxidation rate (AOR) and ciprofloxacin biodegradation rate. These jointly confirmed the importance of the AOB-induced cometabolism in ciprofloxacin biodegradation, with adsorption and metabolic degradation pathways playing minor roles. The continuous exposure of AOB to ciprofloxacin led to decreases of ammonia monooxygenase (AMO) activities and AOR. The antibacterial effects of ciprofloxacin and its biodegradation products were further evaluated and the results revealed that biodegradation products of ciprofloxacin exhibited less toxicity compared to the parent compound, implying the potential application of cometabolism in alleviation of antimicrobial activity. The findings provided new insights into the AOB-induced cometabolic biodegradation of fluoroquinolone antibiotics.

Synergetic degradation of Methylene Blue through photocatalysis and Fenton reaction on two-dimensional molybdenite-Fe.

The greatest problem in conventional Fenton reaction is the slow production of ROS (reactive oxygen species) because of the inefficient Fe3+/Fe2+ conversion. Based on the extraordinary photo-response property of two-dimensional molybdenite (2DM), photogenerated electrons can be easy separated to accelerate the regeneration of Fe2+. In this work, Fe2+-anchored 2DM (2DM-Fe) was prepared and used as a heterogeneous Fenton catalyst to investigate the degradation efficiency to Methylene Blue (MB) in the presence of light. According to experimental results, 2DM-Fe exhibited extraordinary catalytic activity in MB elimination, which ascribed to the synergetic effect of photogenerated carriers and anchored Fe2+ to H2O2 activation. In addition, 2DM-Fe showed nearly 100% degradation efficiency to MB within 5 cycles with slight leaching amount of Mo and Fe ions, implying the strong stability and reusability in H2O2 system. Furthermore, the influences of H2O2 and 2DM-Fe dosages, pH values as well as the degradation efficiency to different dyes were also investigated. According to quenching experiments and EPR (electron paramagnetic resonance) test, the degradation mechanism of MB mainly ascribed to the oxidation of HO• and •O2-. This finding provides a novel strategy to design rational Fenton catalyst and has great significance to water remediation in the future.

Role of Montmorillonite, Kaolinite, or Illite in Pyrite Flotation: Differences in Clay Behavior Based on Their Structures.

It is widely acknowledged that clay minerals have detrimental effects on the process of flotation, but the mechanisms involved are still not fully understood. In this work, the effects of montmorillonite, kaolinite, and illite on pyrite flotation were investigated from the perspective of various structures of clay minerals. Flotation tests suggested that the detrimental effect of clay minerals on the flotation of pyrite increased as follows: montmorillonite > kaolinite > illite. With the help of rheology measurements, it was found that montmorillonite significantly increased pulp viscosity, which in turn substantially reduced pyrite recovery and grade. Scanning electron microscopy (SEM) images suggested that montmorillonite formed the "house-of-cards" structure by edge-to-edge and edge-to-face contact, while kaolinite and illite platelets were associated mainly in the face-to-face mode. In addition, it was clearly observed by SEM-energy dispersive spectrometry that montmorillonite and kaolinite coat on the pyrite surfaces, which would lower the surface hydrophobicity of pyrite. Kaolinite covered much larger area of pyrite surface than montmorillonite owing to the positive charge occurring at the exposed aluminum-oxygen octahedral sheet of kaolinite. Although illite has a similar 2:1 structure to montmorillonite, it showed little or no effect on pyrite flotation, which was attributed to its poor swelling nature. These findings shed light on the root cause of the adverse effect of clay minerals on pyrite flotation and are expected to provide theoretical guidance for mitigating the negative effects on flotation caused by clays.

Salt coagulation or flocculation? In situ zeta potential study on ion correlation and slime coating with the presence of clay: A case of coal slurry aggregation.

The aggregation state of mineral slurry by coagulant with the presence of clay nanosheets appears similar to a flocculation gel with the absence of flocculant. The interactions between particles in mixed clay and quartz minerals systems are influenced by the interactions of ion correlation and slime coating, which creates zeta potential variation. Particle concentration has a substantial effect on zeta potential, and coal slurry has a relative high particle concentration. To realize an in situ aggregation study, zeta potential measurement of coal slurry was performed using electrokinetic sonic amplitude (ESA) without dilution at different calcium ion concentrations and pH values. The zeta potentials of three minerals commonly occurring in coal slurry (quartz, kaolinite and montmorillonite) with similar particle concentrations were also measured. The result suggests that aggregation of coal slurry by calcium ions in the presence of clay minerals belongs to fluctuation. The ion correlation and slime coating could be detected by ESA with a decrease in zeta potential under high calcium ion concentration conditions. The face-face coagulated clay nanosheets were formed by ion correlation, acting as a "flocculant chain". The adsorption force between the "flocculant" and particles is described as a slime coating. This flocculation process is referred to as "salt-clay-coagulation-flocculation" (SCCF). During ion correlation, rearrangement of the electric double layer between face-face spaces causes a reduction of the zeta potential. The super-fine negatively charged clay nanosheets might coat onto the quartz particle surfaces under the effect of electrostatic attraction force and Ca2+ ion correlation. Quartz and clay minerals were oppositely charged because the special adsorption of calcium ions on the clay basal face was restricted in hexatomic rings.

Preparation of Montmorillonite Nanosheets through Freezing/Thawing and Ultrasonic Exfoliation.

The exfoliation of layered montmorillonite (MMT) into mono- or few-layer sheets is of significance for both fundamental studies and potential applications. In this report, exfoliated MMT nanosheets with different aspect ratios have been prepared via a new freezing/thawing-ultrasonic exfoliation method. Freezing/thawing processing can exfoliate MMT tactoids with low efficiency while virtually retaining the original lateral size. The ultrasonic method has better exfoliation efficiency but tends to damage the nanosheets. By combining them and reasonably controlling the cycle index of freezing/thawing and ultrasonic power, the MMT nanosheets with different aspect ratios have been prepared efficiently. Such a unique exfoliation method has broad applicability for layered materials to produce monolayer nanosheets on a large scale.

Heterotrophic denitrifiers growing on soluble microbial products contribute to nitrous oxide production in anammox biofilm: Model evaluation.

In this work, a model framework was constructed to assess and predict nitrous oxide (N2O) production, substrate and microbe interactions in an anammox biofilm bioreactor. The anammox kinetics were extended by including kinetics of autotrophic soluble microbial products (SMP) formation, which consisted of utilization-associated products (UAP) and biomass-associated products (BAP). Heterotrophic bacteria growing on UAP, BAP and decay released substance (SS) were modelled to perform four-step sequential reductions from nitrate to dinitrogen gas. N2O was modelled as an intermidiate of heterotrophic denitrification via three pathways with UAP, BAP and SS as the electron donors. The developed model framework was evaluated using long-term operational data from an anammox biofilm reactor and satisfactorily reproduced effluent nitrogen and SMP as well as N2O emission factors under different operational conditions. The modeling results revealed that N2O was mainly produced with UAP as the electron donor while BAP and SS play minor roles. Heterotrophic denitrifiers growing on UAP would significantly contribute to N2O emission from anammox biofilm reactor even though heterotrophs only account for a relatively small fraction of active biomass in the anammox biofilm. Comprehensive simulations were conducted to investigate the effects of N loading rate and biofilm thickness, which indicated that maintaining a low N loading rate and a thick biofilm thickness were essential for high total nitrogen removal efficiency and low N2O emission.

Preparation and characterization of self-assembly hydrogels with exfoliated montmorillonite nanosheets and chitosan.

Novel montmorillonite-nanosheet/chitosan (MMTNS/CS) hydrogels fabricated via the self-assembly of exfoliated MMTNS and CS chains were investigated. The exfoliation of MMTNS, self-assembly mechanism and structure of MMTNS/CS hydrogels were characterized by an atomic force microscope, scanning electron microscope, transmission electron microscope, Fourier transform infrared spectroscope, energy-dispersive x-ray spectroscope and Brunauer-Emmett-Teller analyzer, respectively. The results indicated that MMT could be easily exfoliated to nanosheets with a thickness of 1 âˆ¼ 5 nm in aqueous solution by an ultrasonic base upon interlayer hydration. The formation mechanism of the self-assembly hydrogels was due to the hydrogen bond (-OH ··· +NH3-) and electrostatic interaction between the MMTNS and CS. The MMTNSs were connected consecutively by CS in-plane to form a huge slice. The porous structure of the hydrogels was controllable by adjusting the MMTNS/CS mass ratio. The hydrogels could be used as adsorbents for sewage treatments, carriers for drugs, microorganisms and catalyzers due to their controllable porous structure and tremendous specific surface area which were derived from the completely exfoliated MMTNS.

AFM study on the adsorption of Hg2+ on natural molybdenum disulfide in aqueous solutions.

The adsorption of Hg2+ on natural molybdenum disulfide has been studied using atomic force microscope (AFM). The AFM imaging clearly illustrated the adsorption of Hg2+ on the surface of molybdenum disulfide, and also hydration layers on the surfaces. It was found that the presence of a hydration layer on molybdenum disulfide surfaces hindered the Hg2+ adsorption. Also, it was observed that the Hg2+ adsorbed appeared in the form of multilayers. The first adsorbed Hg2+ layer might be mainly attributed to the complexation of Hg2+ with S atoms exposed on molybdenum disulfide surfaces, while the second one might be due to the electrostatic interaction between negatively charged molybdenum disulfide and the cation Hg2+.

Novel MoS2/montmorillonite hybrid aerogel encapsulated PEG as composite phase change materials with superior solar-thermal energy harvesting and storage.

Phase change materials (PCMs) offer significant advantages in energy conversion and storage by facilitating the storage and release of thermal energy during phase transition processes. However, challenges such as leakage during PCM phase transitions and poor light absorption properties have constrained their application in the field of photothermal energy storage. In this study, Montmorillonite (Mt) and molybdenum disulfide (MoS2) has been used to design and synthesize hybrid aerogels (MoS2/Mt) boasting high mechanical strength and excellent photothermal conversion performance. These aerogels are then used to encapsulate polyethylene glycol (PEG) to prepare composite PCMs with outstanding solar-thermal conversion and storage performances. The results show that the synthesized MoS2/Mt-PEG composite PCMs exhibit high enthalpies of melting and solidification of 169.16 J/g and 170.78 J/g, respectively, while the aerogel supporting material has a high compressive modulus of 1.96 MPa. Moreover, the composite material displayed excellent thermal stability and leakage resistance after undergoing 30 melting-cooling cycles. Furthermore, the incorporation of MoS2 imparted outstanding light absorption properties to the MoS2/Mt-PEG composite, resulting in a high light absorption and photothermal conversion-storage efficiency of 93.4 % and 96.47 %, respectively. Synthesized composite PCMs also demonstrate outstanding performance in solar-thermal-electricity conversion, achieving a voltage output of 458 mV under illumination conditions and maintaining a sustainable voltage output even after removing the light source. Thus, the composite PCMs prepared in this work can meet the requirements of high enthalpy, effective leakage prevention, efficient solar-thermal conversion and solar-thermal-electricity conversion performance, thereby presenting potential applications in practical solar energy collection, conversion, and storage.

Highly selective recovery of gold and silver from E-waste via stepwise electrodeposition directly from the pregnant leaching solution enabled by the MoS2 cathode.

The recycling of electronic waste, i.e., waste Printed Circuit Boards (WPCBs), provides substantial environmental and economic advantages. In fact, the concentration of valuable precious and base metals in WPCBs is even higher compared to those found in mined ores. Nevertheless, it is still challenging to selectively extract precious metals with low concentrations from the pregnant leaching solution, due to the co-deposition of base metals, like Cu, which have higher concentrations. In this research, stepwise recovery of precious metals and copper directly from WPCBs thiosulfate leaching solution was facilitated by the Ti cathode coated with MoS2 (MoS2/Ti). The in-situ enrichment of Au(S2O3)23- and Ag(S2O3)23- at the surface of MoS2 enables the high efficiency and selectivity of electrodeposition, which has been confirmed through COMSOL Multiphysics simulations and visualization. As a result, the first-step electrodeposition at 0.6 V recovered 92.44 % Au and 98.18 % Ag without any co-deposition of Cu. Subsequently, the second-step recovery employed a constant current of 0.03 A, achieving 100 % recovery of copper within 12 h. Furthermore, this study optimized the reduction potential, NH3·H2O concentration, and S2O32- concentration for the stepwise electrodeposition process. These findings provide valuable insights for establishing a closed loop circular economy in the electronics industry.

Boron/nitrogen-trapping and regulative electronic states around Ru nanoparticles towards bifunctional hydrogen production.

Developing a straightforward and general strategy to regulate the surface microenvironment of a carbon matrix enriched with N/B motifs for efficient atomic utilization and electronic state of metal sites in bifunctional hydrogen production via ammonia-borane hydrolysis (ABH) and water electrolysis is a persistent challenge. Herein, we present a simple, green, and universal approach to fabricate B/N co-doped porous carbons using ammonia-borane (AB) as a triple functional agent, eliminating the need for hazardous and explosive functional agents and complicated procedures. The pyrolysis of AB induces the regulation of the surface microenvironment of the carbon matrix, leading to the formation of abundant surface functional groups, defects, and pore structures. This regulation enhances the efficiency of atom utilization and the electronic state of the active component, resulting in improved bifunctional hydrogen evolution. Among the catalysts, B/N co-doped vulcan carbon (Ru/BNC) with 2.1 wt% Ru loading demonstrates the highest performance in catalytic hydrogen production from ABH, achieving an ultrahigh turnover frequency of 1854 min-1 (depending on the dispersion of Ru). Furthermore, this catalyst shows remarkable electrochemical activity for hydrogen evolution in alkaline water electrolysis with a low overpotential of 31 mV at 10 mA cm-2. The present study provides a simple, green, and universal method to regulate the surface microenvironment of various carbons with B/N modulators, thereby adjusting the atomic utilization and electronic state of active metals for enhanced bifunctional hydrogen evolution.

Attachment of various-shaped polystyrene microplastics to silica surfaces: Experimental validation of the equivalent Cassini oval extended DLVO model.

Microplastics (MPs) vary in shape and surface characteristics in the environment. The attachment of MPs to surfaces can be studied using the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. However, this theory does not account for the shape MPs. Therefore, we investigated the attachment of spherical, pear-shaped, and peanut-shaped polystyrene MPs to quartz sand in NaCl and CaCl2 solutions using batch tests. The attachment of MPs to quartz sand was quantified using the attachment efficiency (alpha). Subsequently, alpha behaviors were interpreted using energy barriers (EBs) and interaction minima obtained from extended DLVO calculations, which were performed using an equivalent sphere model (ESM) and a newly developed equivalent Cassini model (ECM) to account for the shape of the MPs. The ESM failed to interpret the alpha behavior of the three MP shapes because it predicted high EBs and shallow minima. The alpha values for spherical MPs (0.62-1.00 in NaCl and 0.48-0.96 in CaCl2) were higher than those for pear- and peanut-shaped MPs (0.01-0.63 in NaCl and 0.02-0.46 in CaCl2, and 0.01-0.59 in NaCl and 0.02-0.40 in CaCl2, respectively). Conversely, the ECM could interpret the alpha behavior of pear- and peanut-shaped MPs either by changes in EBs or interaction minima as a function of orientation angles and electrolyte ionic strength. Therefore, the particle shape must be considered to improve the attachment analyses.

Regulating Chemisorption and Electrosorption Activity for Efficient Uptake of Rare Earth Elements in Low Concentration on Oxygen-Doped Molybdenum Disulfide.

Recovery of rare earth elements (REEs) with trace amount in environmental applications and nuclear energy is becoming an increasingly urgent issue due to their genotoxicity and important role in society. Here, highly efficient recovery of low-concentration REEs from aqueous solutions by an enhanced chemisorption and electrosorption process of oxygen-doped molybdenum disulfide (O-doped MoS2) electrodes is performed. All REEs could be extremely recovered through a chemisorption and electrosorption coupling (CEC) method, and sorption behaviors were related with their outer-shell electrons. Light, medium, and heavy ((La(III), Gd(III), and Y(III)) rare earth elements were chosen for further investigating the adsorption and recovery performances under low-concentration conditions. Recovery of REEs could approach 100% under a low initial concentration condition where different recovery behaviors occurred with variable chemisorption interactions between REEs and O-doped MoS2. Experimental and theoretical results proved that doping O in MoS2 not only reduced the transfer resistance and improved the electrical double layer thickness of ion storage but also enhanced the chemical interaction of REEs and MoS2. Various outer-shell electrons of REEs performed different surficial chemisorption interactions with exposed sulfur and oxygen atoms of O-doped MoS2. Effects of variants including environmental conditions and operating parameters, such as applied voltage, initial concentration, pH condition, and electrode distance on adsorption capacity and recovery of REEs were examined to optimize the recovery process in order to achieve an ideal selective recovery of REEs. The total desorption of REEs from the O-doped MoS2 electrode was realized within 120 min while the electrode demonstrated a good cycling performance. This work presented a prospective way in establishing a CEC process with a two-dimensional metal sulfide electrode through structure engineering for efficient recovery of REEs within a low concentration range.

Potential Evaluation for Preparing Geopolymers from Quartz by Low-Alkali Activation.

Alkali fusion of granite sawdust at a high alkali dosage can significantly improve geopolymerization activity, but also result in a high alkali consumption and a poor geopolymer performance. In this work, quartz, the most inert component in granite sawdust, was selected to explore the effect of low-alkali activation on its reactivity and the compressive strength of geopolymer. It was found that the amount of activated quartz is mainly determined by the amount of alkali used for activation. The surface of a quartz particle can be effectively activated by an alkali fusion process at a low alkali dosage of 5%. The metakaolin-based geopolymer synthesized with quartz activated by an alkali dosage of 5% shows a high compressive strength of 41 MPa, which can be attributed to the enhanced interfacial interaction between quartz and the geopolymer gel, suggesting that low-alkali activation is a potential way to improve the geopolymerization ability of granite sawdust.

Dewatering behavior and regulation mechanism of montmorillonite nanosheet in aqueous solution.

Two-dimensional montmorillonite nanosheet (MMTNS) is desirable building block for fabricating multifunctional materials as due to its extraordinary properties. In practical applications, however, the concentration of MMTNS prepared by exfoliation is normally too low to be used for material assembling. The general thermal-concentration method is effective, however, it can be time-consuming and require a lot of energy. In this case, the remarkable dispersion stability of MMTNS is worth noting. Herein, the extraordinary dispersion stability of MMTNS derived from electrostatic and hydration repulsion was firstly revealed by molecular dynamics (MD) simulation, which caused the poor dewatering of MMTNS. Further, based on the surface and structural chemistry of MMTNS, a series of strategies, involving charge and cross-linked structure regulation on the edge surface, as well as electrical double-layer modulation and calcification modification based on the electrolytes, were proposed to inhibit the dispersion and enhance the aggregation of MMTNS. Intriguingly, a novel chemical, Tetraethylenepentamine (TEPA) was applied in the dewatering of MMTNS. The TEPA not only act as a cross-linker to bond with MMTNS into an easy-to-dewatering 3D network structure, but also act as a switch for effortless viscosity tuning. Meanwhile, the dual function of electrolytes for electrical double layer compression and calcification modification of MMTNS was investigated by DLVO theory and structural analyses. This work offers explicit directions for improving the dewatering performance of MMTNS to meet the requirements of practical implementation.