Characterization of hard- and softwood biochars pyrolyzed at high temperature.

A wide range of waste biomass/waste wood feedstocks abundantly available at mine sites provide the opportunity to produce biochars for cost-effective improvement of mine tailings and contaminated land at metal mines. In the present study, soft- and hardwood biochars derived from pine and jarrah woods at high temperature (700 °C) were characterized for their physiochemical properties including chemical components, electrical conductivity, pH, zeta potential, cation-exchange capacity (CEC), alkalinity, BET surface area and surface morphology. Evaluating and comparing these characteristics with available data from the literature have affirmed the strong dictation of precursor type on the physiochemical properties of the biochars. The pine and jarrah wood feedstocks are mainly different in their proportions of cellulose, hemicellulose and lignin, resulting in biochars with heterogeneous physiochemical properties. The hardwood jarrah biochar exhibits much higher microporosity, alkalinity and electrostatic capacity than the softwood pine. Correlation analysis and principal component analysis also show a good correlation between CEC-BET-alkalinity, and alkalinity-ash content. These comprehensive characterization and analysis results on biochars' properties from feedstocks of hardwood (from forest land clearance at mine construction) and waste pine wood (from mining operations) will provide a good guide for tailoring biochar functionalities for remediating metal mine tailings. The relatively inert high-temperature biochars can be stored for a long term at mine closure after decades of operations.

Effect of different co-foaming agents on PFAS removal from the environment by foam fractionation.

Per- and poly-fluoroalkyl substances (PFAS) are recalcitrant, synthetic chemicals that are ubiquitous in the environment because of their widespread use in a variety of consumer and industrial products. PFAS contamination has become an increasing issue in recent years, which needs to be urgently addressed. Foam fractionation is emerging as a potential remediation option that removes PFAS by adsorption to the surface of rising air bubbles which are removed from the system as a foam. PFAS concentrations in the environment are often not sufficient to allow for formation of a foam by itself and often a co-foaming agent is required to be added to enhance the foamability of the solution. In this study, the effect of different classes of co-foaming agents, anionic, non-ionic, zwitterionic and cationic surfactants on the removal of PFAS with varying fluorocarbon chain length from 3 to 8 in a foam fractionation process have been investigated. Evaluation of the air-water interface partitioning coefficient (k') in addition with surface tension and PFAS removal results support the contention that using a co-foaming agent with the opposite charge to the PFAS in question significantly facilitates the adsorption of PFAS to the air-water interface, enhancing the efficiency of the process. Using the non-ionic surfactant (no headgroup electrostatic interaction with PFAS), as a reference, it was observed, in terms of PFAS separation and rate of PFAS removal, that anionic co-surfactant performed worst, zwitterionic was better, and cationic co-surfactant performed best. All of the PFAS species were able to be removed below the limit of detection (0.05 µg/L) after 45 minutes of foaming time with the cationic surfactant.

Foam fractionation of per- and polyfluoroalkyl substances (PFASs) in landfill leachate using different cosurfactants.

Foam fractionation is one solution to recover per- and polyfluoroalkyl substances (PFASs) from aqueous sources. The separation process is based on the sorption of PFASs to the air-water interface of bubbles. In many practical cases, the PFAS concentration in the polluted liquid is too low to sustain foam formation and requires the support of a cosurfactant not only to act as a collector of PFAS but also to produce and sustain foam for effective separation. However, there is a lack of information regarding the appropriate choice of cosurfactant and its quantitative effect on the interfacial partitioning of PFASs on the air bubbles. This study is directed to (i) evaluate the effectiveness of four cosurfactants with different-charged headgroups (i.e., anionic, cationic, zwitterionic and nonionic) for foam fractionation of PFASs, and (ii) estimate the air-water interfacial partitioning (Ki) of PFASs in the presence of four different types of cosurfactants. The Ki values span over 4 orders of magnitude with good correlation with PFASs molar volume. All of the cosurfactants were effective for the removal of the long chain PFASs (1.2-4 logs). The cationic and zwitterionic surfactants have oppositely charged head groups with respect to the anionic PFASs and therefore facilitate increased separation due to charge interactions. Some short chain PFASs (e.g., Perfluorobutanesulfonic acid (PFBS), Perfluoropentanesulfonic acid (PFPeS)) can be effectively removed using cationic and zwitterionic cosurfactants.

Using foam fractionation to estimate PFAS air-water interface adsorption behaviour at ng/L and µg/L concentrations.

PFAS are biologically recalcitrant compounds that are persistent in the environment and have subsequently contaminated groundwater, landfill leachate and surface water. Due to their persistence and toxicity, there are environmental concentration limits imposed on some PFAS compounds that extend down to a few nanograms per litre and even proposals for reducing these to picogram per litre levels. Since PFAS concentrates at water-air interfaces as a result of their amphiphilic nature, this characteristic is important for the successful modelling and prediction of transport behaviour of PFAS through various systems. Here we present a procedure for using a foam fractionation method to experimentally determine the PFAS adsorption behaviour at ng/L and µg/L concentrations in the presence of salts. The equilibrium air-water adsorption coefficients for PFHxS and PFOA at different salinities and concentrations are experimentally shown to be constant across the range of PFAS concentrations investigated (approx. 0.1-100 µg/L). The adsorption isotherms may consequently be modelled by Henry or Langmuir style equations at these low concentrations.

Study on the controllable scale-up growth of vertically-aligned carbon nanotube arrays.

Vertically aligned carbon nanotubes (VA-CNTs) with high purity have been grown on quartz substrate via the gas phase catalytic chemical vapour deposition (CVD) by using ferrocene as the catalyst source and camphor as the carbon source. The effects of catalyst concentration, flow rate and water assistance on the morphology and structure of VA-CNTs are investigated by SEM, TEM, Raman and XPS characterizations. Under the optimized CVD conditions with modest ferrocene concentration and flow rate, dense and well VA-CNT arrays have been obtained. The water concentration should be controlled to improve CNTs alignment and impurity without damaging the walls of CNTs.

Integrating a Top-Gas Recycling and CO2 Electrolysis Process for H2-Rich Gas Injection and Reduce CO2 Emissions from an Ironmaking Blast Furnace.

Introducing CO2 electrochemical conversion technology to the iron-making blast furnace not only reduces CO2 emissions, but also produces H2 as a byproduct that can be used as an auxiliary reductant to further decrease carbon consumption and emissions. With adequate H2 supply to the blast furnace, the injection of H2 is limited because of the disadvantageous thermodynamic characteristics of the H2 reduction reaction in the blast furnace. This paper presents thermodynamic analysis of H2 behaviour at different stages with the thermal requirement consideration of an iron-making blast furnace. The effect of injecting CO2 lean top gas and CO2 conversion products H2-CO gas through the raceway and/or shaft tuyeres are investigated under different operating conditions. H2 utilisation efficiency and corresponding injection volume are studied by considering different reduction stages. The relationship between H2 injection and coke rate is established. Injecting 7.9-10.9 m3/tHM of H2 saved 1 kg/tHM coke rate, depending on injection position. Compared with the traditional blast furnace, injecting 80 m3/tHM of H2 with a medium oxygen enrichment rate (9%) and integrating CO2 capture and conversion reduces CO2 emissions from 534 to 278 m3/tHM. However, increasing the hydrogen injection amount causes this iron-making process to consume more energy than a traditional blast furnace does.

Restaurant oil and grease management in Hong Kong.

Oil and grease (O&G) in wastewater can be considered as two parts or proportion contained in emulsion which exceeded O&G standard. Most of oil becomes emulsified with water when they pass through grease trap and discharged in the effluents. Thus, it may indicate that either treatment of grease traps or standards for O&G content stipulated in technical memorandum of Water Pollution Control Ordinance (WPCO) do not reflect the actual situation. Existing grease traps should be upgraded to meet the requirements of WPCO. Alternative technologies need to be developed to tackle this unsolved problem. Good management and practices are also important to ensure proper collection and waste recycling rather than just disposing effluent into drains. Collected O&G content can be recycled as valuable products such as biofuel, flotation agent, or other derivatives. This approach not only protects the environment by improving water quality, it also encourages large flow restaurant operators to recycle oil and grease content towards cleaner production.

Effect of selected monovalent salts on surfactant stabilized foams.

Surfactant-stabilized foams have been at the centre of scientific research for over a century due to their ubiquitous applications in different industries. Many of these applications involve inorganic salts either due to their natural presence (e.g. use of seawater in froth floatation) or their addition (e.g. in cosmetics) to manipulate foam characteristics for the best outcomes. This paper provides a clear understanding of the effect of salts on surfactant-stabilized foams through a critical literature survey of this topic. Available literature shows a double effect of salts (LiCl, NaCl and KCl) on foam characteristics in the presence of surfactants. To elucidate the underlying mechanisms of the stabilizing effect of salts on foams, the effect of salts on surfactant-free thin liquid films is first discussed, followed by a discussion on the effect of salts on surfactant-stabilized foams with the focus on anionic surfactants. We discuss two distinctive salt concentrations, salt transition concentration in surfactant-free solutions and salt critical concentration in surfactant-laden systems to explain their effects. Using the available data in literature supported by dedicated experiments, we demonstrate the destabilizing effect of salts on foams at and above their critical concentrations in the presence of anionic surfactants. This effect is attributed to retarding the adsorption of the surfactant molecules at the interface due to the formation of nano and micro-scale aggregates.

Nanostructured NiMoS2/Carbon Catalysts for Syngas Conversion to Higher Alcohols.

Syngas conversion to higher alcohols remains a very attractive alternative due to the abundance of syngas feedstock, such as renewable carbon and waste-carbon resources. Catalysts suitable for syngas conversion still show low selectivity to alcohols. In this article, we present nanostructured NiMoS2 and CoMoS2 catalysts supported on activated carbon pellets and design strategies to improve its selectivity towards higher alcohols. Activated carbon pellets were treated with concentrated HNO3 to enlarge porous channels and enable better dispersion of NiMoS2 and CoMoS2. These treatment steps lead to a formation of nanostructured NiMoS2 and CoMoS2 catalysts and promoted higher selectivity to ethanol, propanol and butanol. BET surface area of 532 m² g-1 was obtained for NiMoS2/Carbon catalysts from the nitrogen physisorption analysis. In catalytic tests, the highest CO conversion (39.1%) was achieved by the NiMoS2/Carbon, whereas the CoMoS2/Carbon showed the highest alcohol selectivity (74.4%). CoMoS2 catalysts supported on activated carbon pellets proved to be highly active towards undesired by-product "filamentous carbon."

Catalyst-Electrolyte Interactions in Aqueous Reline Solutions for Highly Selective Electrochemical CO2 Reduction.

Invited for this month's cover is the group of Tom Rufford at the University of Queensland. The image shows how choline chloride and urea in a reline solution interact with the surface of a silver cathode to enhance the selectivity of electrochemical CO2 reduction to CO. The Full Paper itself is available at 10.1002/cssc.201902433.

Catalyst-Electrolyte Interactions in Aqueous Reline Solutions for Highly Selective Electrochemical CO2 Reduction.

Achieving high product selectivities is one challenge that limits viability of electrochemical CO2 reduction (CO2 R) to chemical feedstocks. Here, it was demonstrated how interactions between Ag foil cathodes and reline (choline chloride + urea) led to highly selective CO2 R to CO with a faradaic efficiency of (96±8) % in 50 wt % aqueous reline at -0.884 V vs. the reversible hydrogen electrode (RHE), which is a 1.5-fold improvement over CO2 R in KHCO3 . In reline the Ag foil was roughened by (i) dissolution of oxide layers followed by (ii) electrodeposition of Ag nanoparticles back on cathode. This surface restructuring exposed low-coordinated Ag atoms, and subsequent adsorption of choline ions and urea at the catalyst surface limited proton availability in the double layer and stabilized key intermediates such as *COOH. These approaches could potentially be extended to other electrocatalytic metals and lower-viscosity deep eutectic solvents to achieve higher-current-density CO2 R in continuous-flow cell electrolyzers.

Modulated Sn Oxidation States over a Cu2O-Derived Substrate for Selective Electrochemical CO2 Reduction.

Pursuing high catalytic selectivity is challenging but paramount for an efficient and low-cost CO2 electrochemical reduction (CO2R). In this work, we demonstrate a significant correlation between the selectivity of CO2R to formate and the duration of tin (Sn) electrodeposition over a cuprous oxide (Cu2O)-derived substrate. A Sn electrodeposition time of 120 s led to a cathode with a formate Faradaic efficiency of around 81% at -1.1 V vs reversible hydrogen electrode (RHE), which was more than 37% higher than those of the Sn foil and the sample treated for 684 s. This result highlights the significant role of the interface between deposited Sn and the cuprous-derived substrate in determining the selectivity of CO2R. High-resolution X-ray photoelectron spectra revealed that the residual cuprous species at the Cu/Sn interfaces could stabilize Sn species in oxidation states of 2+ and 4+, a mixture of which is essential for a selective formate conversion. Such modulation effects likely arise from the moderate electronegativity of the cuprous species that is lower than that of Sn2+ but higher than that of Sn4+. Our work highlights the significant role of the substrate in the selectivity of the deposited catalyst and provides a new avenue to advance selective electrodes for CO2 electrochemical reduction.

Phosphate removal from wastewater using red mud.

Red mud, a waste residue of alumina refinery, has been used to develop effective adsorbents to remove phosphate from aqueous solution. Acid and acid-thermal treatments were employed to treat the raw red mud. The effects of different treatment methods, pH of solution and operating temperature on adsorption have been examined in batch experiments. It was found that all activated red mud samples show higher surface area and total pore volume as well as higher adsorption capacity for phosphate removal. The red mud with HCl treatment shows the highest adsorption capacity among all the red mud samples, giving adsorption capacity of 0.58 mg P/g at pH 5.5 and 40 degrees C. The adsorption capacity of the red mud adsorbents decreases with increase of pH. At pH 2, the red mud with HCl treatment exhibits adsorption of 0.8 mg P/g while the adsorption can be lowered to 0.05 mg P/g at pH 10. However, the adsorption is improved at higher temperature by increasing 25% from 30 to 40 degrees C. The kinetic studies of phosphate adsorption onto red mud indicate that the adsorption mainly follows the parallel first-order kinetics due to the presence of two acidic phosphorus species, H(2)PO(4)(-) and HPO(4)(2-). An analysis of the adsorption data indicates that the Freundlich isotherm provides a better fitting than the Langmuir model.

Ionic Liquids as the MOFs/Polymer Interfacial Binder for Efficient Membrane Separation.

Obtaining strong interfacial affinity between filler and polymer is critical to the preparation of mixed matrix membranes (MMMs) with high separation efficiency. However, it is still a challenge for micron-sized metal organic frameworks (MOFs) to achieve excellent compatibility and defect-free interface with polymer matrix. Thin layer of ionic liquid (IL) was immobilized on micron-sized HKUST-1 to eliminate the interfacial nonselective voids in MMMs with minimized free ionic liquid (IL) in polymer matrix, and then the obtained IL decorated HKUST-1 was incorporated into 4,4'-(hexafluoroisopropylidene)diphthalic anhydride-2,3,5,6-tetramethyl-1,3-phenyldiamine (6FDA-Durene) to fabricate MMMs. Acting as a filler/polymer interfacial binder, the favorable MOF/IL and IL/polymer interaction can facilitate the enhancement of MOF/polymer affinity. Compared to MMM with only HKUST-1 incorporation, MMM with IL decorated HKUST-1 succeeded in restricting the formation of nonselective interfacial voids, leading to an increment in CO2 selectivity. The IL decoration method can be an effective approach to eliminate interfacial voids in MMMs, extending the filler selection to a wide range of large-sized fillers.

Copper and zinc adsorption by softwood and hardwood biochars under elevated sulphate-induced salinity and acidic pH conditions.

Biochar adsorption may lower concentrations of soluble metals in pore water of sulphidic Cu/Pb-Zn mine tailings. Unlike soil, high levels of salinity and soluble cations are present in tailing pore water, which may affect biochar adsorption of metals from solution. In the present study, removal of soluble copper (Cu) and zinc (Zn) ions by soft- (pine) and hard-wood (jarrah) biochars pyrolysed at high temperature (about 700 °C) was evaluated under typical ranges of pH and salinity conditions resembling those in pore water of sulphidic tailings, prior to their direct application into the tailings. Surface alkalinity, cation exchange capacity, and negative surface charge of biochars affected Cu and Zn adsorption capacities. Quantitative comparisons were provided by fitting the adsorption equilibrium data with either the homogeneous or heterogeneous surface adsorption models (i.e. Langmuir and Freundlich, respectively). Accordingly, the jarrah biochar showed higher Cu and Zn adsorption capacity (Qmax=4.39 and 2.31 mg/g, respectively) than the softwood pine biochar (Qmax=1.47 and 1.00 mg/g). Copper and Zn adsorption by the biochars was favoured by high pH conditions under which they carried more negative charges and Cu and Zn ions were predicted undergoing hydrolysis and polymerization. Within the tested range, salinity had relatively weak effects on the adsorption, which perhaps influenced the surface charge and induced competition for negative charged sites between Na(+) and exchangeable Ca(2+) and/or heavy metal ions. Large amounts of waste wood/timber at many mine sites present a cost-effective opportunity to produce biochars for remediation of sulphidic tailings and seepage water.

Mixed-Matrix Membranes with Metal-Organic Framework-Decorated CNT Fillers for Efficient CO2 Separation.

Carbon nanotube (CNT) mixed-matrix membranes (MMMs) show great potential to achieve superior gas permeance because of the unique structure of CNTs. However, the challenges of CNT dispersion in polymer matrix and elimination of interfacial defects are still hindering MMMs to be prepared for high gas selectivity. A novel CNT/metal-organic framework (MOF) composite derived from the growth of NH2-MIL-101(Al) on the surface of CNTs have been synthesized and applied to fabricate polyimide-based MMMs. Extra amino groups and active sites were introduced to external surface of CNTs after MOF decoration. The good adhesion between the synthesized CNT-MIL fillers and polymer phase was observed, even at a high filler loadings up to 15%. Consequently, MMMs containing the synthesized MOF/CNT composite exhibit not only a large CO2 permeability but also a high CO2/CH4 selectivity; the combined performance of permeability and selectivity is even above the Robeson upper bound. The strategy of growing MOFs on CNTs can be further utilized to develop a more effective approach to further improve MMM performance through the decoration of MOFs on existing fillers that have high selectivity to specific gas.

Synthesis and characterization of three amino-functionalized metal-organic frameworks based on the 2-aminoterephthalic ligand.

The incorporation of Lewis base sites and open metal cation sites into metal-organic frameworks (MOFs) is a potential route to improve selective CO2 adsorption from gas mixtures. In this study, three novel amino-functionalized metal-organic frameworks (MOFs): Mg-ABDC [Mg3(ABDC)3(DMF)4], Co-ABDC [Co3(ABDC)3(DMF)4] and Sr-ABDC [Sr(ABDC)(DMF)] (ABDC = 2-aminoterephthalate) were synthesized by solvothermal reactions of 2-aminoterephthalic acid (H2ABDC) with magnesium, cobalt and strontium metal centers, respectively. Single-crystal structure analysis showed that Mg-ABDC and Co-ABDC were isostructural compounds comprising two-dimensional layered structures. The Sr-ABDC contained a three-dimensional motif isostructural to its known Ca analogue. The amino-functionalized MOFs were characterized by powder X-ray diffraction, thermal gravimetric analysis and N2 sorption. The CO2 and N2 equilibrium adsorption capacities were measured at different temperatures (0 and 25 °C). The CO2/N2 selectivities of the MOFs were 396 on Mg-ABDC, 326 on Co-ABDC and 18 on Sr-ABDC. Both Mg-ABDC and Co-ABDC exhibit high heat of CO2 adsorption (>30 kJ mol(-1)). The Sr-ABDC displays good thermal stability but had a low adsorption capacity resulting from narrow pore apertures.

Interparticle van der Waals force in powder flowability and compactibility.

Particle flowability and compactibility are the two critical process parameters tested when a pharmaceutical material is formulated for a tabletting process. These behavioral descriptions are strongly affected by geometrical, physical, chemical and mechanical particle properties, as well as operational conditions. The property influences are broadly known in a qualitative sense, but have largely escaped fundamental quantitative description. Various measurement methods have been separately developed for each of these properties which provide comparative indices to assist in process and formulation design. This paper seeks to establish the connections between interparticle van der Waals force and both flowability and compactibility, and therefore also the inter-relations between the two apparently distinct properties. Paracetamol and the excipients often associated with it for tabletting are used as test materials to provide an initial validation of the theoretical development. These powders are well-characterized and known to be particularly difficult with respect to flowability and compactibility.

In situ synthesis of zeolitic imidazolate frameworks/carbon nanotube composites with enhanced CO2 adsorption.

A series of ZIF-8 and hydroxyl-functionalized carbon nanotube (CNT) composites were successfully synthesized by the solvothermal method. The obtained ZIF-8/CNT composites were characterized by XRD, SEM, TGA and N2 adsorption at 77 K. The contents of ZIF-8 and CNTs in the composites were calculated from thermal analysis data. CO2 and N2 adsorption at 273 K on the composites was also investigated and compared. The ZIF-8 particles in the composites exhibit similar crystal structures and morphology to those of pure ZIF-8, but display enhanced thermal stability. The surface areas and pore volumes of the ZIF-8/CNT composites are higher than the values calculated for hypothetical physical mixtures, and the synergetic effect between ZIF-8 and CNTs can be proposed. This phenomenon demonstrates that the incorporation of CNTs into ZIF-8 can facilitate the nucleation and crystallization of ZIF-8. As a result, the composites with an optimal CNT content (3.63 wt%) show improved CO2 adsorption capacity and higher relative selectivity for CO2/N2 compared with pure ZIF-8.