Facile Fabrication of Monodispersed Carbon Sphere: A Pathway Toward Energy-Efficient Direct Air Capture (DAC) Using Amino Acids.

Direct removal of carbon dioxide (CO2 ) from the atmosphere, known as direct air capture (DAC) is attracting worldwide attention as a negative emission technology to control atmospheric CO2 concentrations. However, the energy-intensive nature of CO2 absorption-desorption processes has restricted deployment of DAC operations. Catalytic solvent regeneration is an effective solution to tackle this issue by accelerating CO2 desorption at lower regeneration temperatures. This work reports a one-step synthesis methodology to prepare monodispersed carbon nanospheres (MCSs) using trisodium citrate as a structure-directing agent with acidic sites. The assembly of citrate groups on the surface of MCSs enables consistent spherical growth morphology, reduces agglomeration and enhances water dispersibility. The functionalization-assisted synthesis produces uniform, hydrophilic nanospheres of 100-600 nm range. This work also demonstrates that the prepared MCSs can be further functionalized with strong Brønsted acid sites, providing high proton donation ability. Furthermore, the materials can be effectively used in a wide range of amino acid solutions to substantially accelerate CO2 desorption (25.6% for potassium glycinate and 41.1% for potassium lysinate) in the DAC process. Considering the facile synthesis of acidic MCSs and their superior catalytic efficiency, these findings are expected to pave a new path for energy-efficient DAC.

Engineered assembly of water-dispersible nanocatalysts enables low-cost and green CO2 capture.

Catalytic solvent regeneration has attracted broad interest owing to its potential to reduce energy consumption in CO2 separation, enabling industry to achieve emission reduction targets of the Paris Climate Accord. Despite recent advances, the development of engineered acidic nanocatalysts with unique characteristics remains a challenge. Herein, we establish a strategy to tailor the physicochemical properties of metal-organic frameworks (MOFs) for the synthesis of water-dispersible core-shell nanocatalysts with ease of use. We demonstrate that functionalized nanoclusters (Fe3O4-COOH) effectively induce missing-linker deficiencies and fabricate mesoporosity during the self-assembly of MOFs. Superacid sites are created by introducing chelating sulfates on the uncoordinated metal clusters, providing high proton donation capability. The obtained nanomaterials drastically reduce the energy consumption of CO2 capture by 44.7% using only 0.1 wt.% nanocatalyst, which is a ∽10-fold improvement in efficiency compared to heterogeneous catalysts. This research represents a new avenue for the next generation of advanced nanomaterials in catalytic solvent regeneration.

Modification of naturally abundant resources for remediation of potentially toxic elements: A review.

Water and soil contamination due to potentially toxic elements (PTEs) represents a critical threat to the global ecosystem and human health. Naturally abundant resources have significant advantages as adsorbent materials for environmental remediation over manufactured materials such as nanostructured materials and activated carbons. These advantages include cost-effectiveness, eco-friendliness, sustainability, and nontoxicity. In this review, we firstly compare the characteristics of representative adsorbent materials including bentonite, zeolite, biochar, biomass, and effective modification methods that are frequently used to enhance their adsorption capacity and kinetics. Following this, the adsorption pathways and sites are outlined at an atomic level, and an in-depth understanding of the structure-property relationships are provided based on surface functional groups. Finally, the challenges and perspectives of some emerging naturally abundant resources such as lignite are examined. Although both unamended and modified naturally abundant resources face challenges associated with their adsorption performance, cost performance, energy consumption, and secondary pollution, these can be tackled by using advanced techniques such as tailored modification, formulated mixing and reorganization of these materials. Recent studies on adsorbent materials provide a strong foundation for the remediation of PTEs in soil and water. We speculate that the pursuit of effective modification strategies will generate remediation processes of PTEs better suited to a wider variety of practical application conditions.

Water-Dispersible Nanocatalysts with Engineered Structures: The New Generation of Nanomaterials for Energy-Efficient CO2 Capture.

The high energy demand of CO2 absorption-desorption technologies has significantly inhibited their industrial utilization and implementation of the Paris Climate Accord. Catalytic solvent regeneration is of considerable interest due to its low operating temperature and high energy efficiency. Of the catalysts available, heterogeneous catalysts have exhibited relatively poor performances and are hindered by other challenges, which have slowed their large-scale deployment. Herein, we report a facile and eco-friendly approach for synthesizing water-dispersible Fe3O4 nanocatalysts coated with a wide range of amino acids (12 representative molecules) in aqueous media. The acidic properties of water-dispersible nanocatalysts can be easily tuned by introducing different functional groups during the hydrothermal synthesis procedure. We demonstrate that the prepared nanocatalysts can be used in energy-efficient CO2 capture plants with ease-of-use, at very low concentrations (0.1 wt %) and with extra-high efficiencies (up to ∼75% energy reductions). They can be applied in a range of solutions, including amino acids (i.e., short-chain, long-chain, and cyclic) and amines (i.e., primary, tertiary, and primary-tertiary mixture). Considering the superiority of the presented water-dispersible nanocatalysts, this technology is expected to provide a new pathway for the development of energy-efficient CO2 capture technologies.

The electro-Fenton regeneration of Granular Activated Carbons: Degradation of organic contaminants and the relationship to the carbon surface.

Electrochemical regeneration of Granular Activated Carbon is an emerging treatment option to restore adsorption capacity in systems designed to remove organic contaminants from aqueous solutions. The electro-Fenton process is one such electrochemical process and it is reviewed along with other members of its family including Photoelectro-Fenton and Heterogeneous electro-Fenton and electro-Fenton like reactions, for its ability to regenerate Granular Activated Carbons contaminated with organics. The behaviour of critical operating parameter such as pH, current, catalyst concentration and initial contaminant concentration are reviewed to find optimal operating conditions. The relationship between electro-Fenton regeneration and the chemical and physical surface of the carbon is also explored. Understanding regeneration mechanisms and the optimal operating conditions enables these technologies to be used commercially and to be scaled-up and treat contaminated waters more efficiently.

Adsorption Behavior of Divalent Metal Ions onto Surface-functionalized Mesoporous Silicate MCM-41 Having Schiff Base Structure.

Surface functionalized mesoporous silicates, MCM-41s, having 3-(2-pyridylmethylideneimino)propyl group (PI-MCM-41) or 3-(2-quinolylmethylideneimino)propyl group (QI-MCM-41) were prepared via Schiff base reaction, and the adsorption behavior of metal ions onto the modified MCM-41s was investigated. The function groups on the modified MCM-41 surface were confirmed by Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and elemental analysis. The metal ions examined, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, and Pb2+, were quantitatively adsorbed on the PI-MCM-41 and QI-MCM-41, except for Mn2+. In the complexation with these metal ions, it was suggested that imine-N and heterocyclic-N atoms act as donor atoms. In addition, it was considered that the hydrophobicity derived from the organo-functional groups modified on MCM-41 contributed to improving the adsorption ability.

Assessment of the electro-Fenton pathway for the removal of naphthalene from contaminated waters in remote regions.

This work investigates the effectiveness of the electro-Fenton reaction for the treatment of wastewaters contaminated with petroleum hydrocarbons. More specific attention was given to field deployment applications in remote regions, such as the sub-Antarctic, where there is a need for low-cost technologies that can aid in remediation efforts. Naphthalene, a high priority pollutant for removal within these regions, was chosen as a model contaminant and treated with inexpensive graphite electrodes to promote the electro-Fenton pathway. Results show that naphthalene can be fully removed from a near-saturated solution, 20 mg/L, in less than 3 h of treatment. The underlying removal mechanisms were identified, and a kinetic model is presented that can accurately predict treatment outcomes at varying operating conditions of applied electric currents, 0-5 mA, and iron(II) concentrations, 0-2.0 mM. Optimal operating conditions for the electro-Fenton pathway were found to be at an applied current of 5 mA and an iron(II) concentration of 0.06 mM; this resulted in a specific energy consumption of 5.6 kWhr/kg of naphthalene removed, low enough to be operated in remote regions via sustainable energy sources.

Cytochrome P450-mediated N-demethylation of noscapine by whole-cell biotransformation: process limitations and strategies for optimisation.

Cytochrome P450 enzymes catalyse reactions of significant industrial interest but are underutilised in large-scale bioprocesses due to enzyme stability, cofactor requirements and the poor aqueous solubility and microbial toxicity of typical substrates and products. In this work, we investigate the potential for preparative-scale N-demethylation of the opium poppy alkaloid noscapine by a P450BM3 (CYP102A1) mutant enzyme in a whole-cell biotransformation system. We identify and address several common limitations of whole-cell P450 biotransformations using this model N-demethylation process. Mass transfer into Escherichia coli cells was found to be a major limitation of biotransformation rate and an alternative Gram-positive expression host Bacillus megaterium provided a 25-fold improvement in specific initial rate. Two methods were investigated to address poor substrate solubility. First, a biphasic biotransformation system was developed by systematic selection of potentially biocompatible solvents and in silico solubility modelling using Hansen solubility parameters. The best-performing biphasic system gave a 2.3-fold improvement in final product titre compared to a single-phase system but had slower initial rates of biotransformation due to low substrate concentration in the aqueous phase. The second strategy aimed to improve aqueous substrate solubility using cyclodextrin and hydrophilic polymers. This approach provided a fivefold improvement in initial biotransformation rate and allowed a sixfold increase in final product concentration. Enzyme stability and cell viability were identified as the next parameters requiring optimisation to improve productivity. The approaches used are also applicable to the development of other pharmaceutical P450-mediated biotransformations.

High-Efficiency Biocatalytic Conversion of Thebaine to Codeine.

An enzymatic biosynthesis approach is described for codeine, the most widely used medicinal opiate, providing a more environmentally sustainable alternative to current chemical conversion, with yields and productivity compatible with industrial production. Escherichia coli strains were engineered to express key enzymes from poppy, including the recently discovered neopinone isomerase, producing codeine from thebaine. We show that compartmentalization of these enzymes in different cells is an effective strategy that allows active spatial and temporal control of reactions, increasing yield and volumetric productivity and reducing byproduct generation. Codeine is produced at a yield of 64% and a volumetric productivity of 0.19 g/(L·h), providing the basis for an industrially applicable aqueous whole-cell biotransformation process. This approach could be used to redirect thebaine-rich feedstocks arising from the U.S. reduction of opioid manufacturing quotas or applied to enable total biosynthesis and may have broader applicability to other medicinal plant compounds.

Electrochemical removal of naphthalene from contaminated waters using carbon electrodes, and viability for environmental deployment.

This work assesses the potential of electrochemical technologies for the treatment of groundwaters contaminated with petroleum hydrocarbons. Specific consideration was given to deployment in Antarctic regions where numerous fuel spills have occurred over the last two centuries, and resources and manual labour for remediation efforts are limited. The polycyclic aromatic hydrocarbon, naphthalene, was a used as a model contaminant and was treated with low-cost, active carbon electrodes to promote the active chlorine degradation pathway. Results showed that 20 mg/L naphthalene solutions could be treated to sufficient standards in less than 3 h of treatment, and that the formation of toxic and chlorinated by-products is not an issue of concern if the appropriate timeframes are used (4 h of treatment). The effects of the applied current (0-160 mA) and electrolyte concentration (0.01-0.1 M NaCl) were evaluated and a dynamic kinetic model proposed and found to be in good agreement with the experimental results. The energy consumption is an important limitation in remote environmental regions where resources are scarce. It was found that an energy usage of 104 kW h/kg of naphthalene removed could be achieved.

Data in brief on CO2 absorption-desorption of aqueous-based amino acid solvents with phase change behaviour.

The data presented in this paper are related to the published research article "Development of aqueous-based phase change amino acid solvents for energy-efficient CO2 capture: The role of antisolvent" [1]. The raw and analyzed data include the equilibrium and kinetics of CO2 absorption, the density and concentration of different CO2-containing species at upper and lower liquid phases, and particle size distribution of solid particles precipitated during CO2 absorption of aqueous and aqueous-based amino acid solvents. In addition, the SEM images of solid precipitates at the end of CO2 absorption are presented. The detailed values of this phase change amino acid solvent are crucial for large-scale implementation of CO2 capture systems with phase change behavior.

Production of metabolites of the anti-cancer drug noscapine using a P450BM3 mutant library.

Cytochrome P450 enzymes are a promising tool for the late-stage diversification of lead drug candidates and can provide an alternative route to structural modifications that are difficult to achieve with synthetic chemistry. In this study, a library of P450BM3 mutants was produced using site-directed mutagenesis and the enzymes screened for metabolism of the opium poppy alkaloid noscapine, a drug with anticancer activity. Of the 18 enzyme mutants screened, 12 showed an ability to metabolise noscapine that was not present in the wild-type enzyme. Five noscapine metabolites were detected by LC-MS/MS, with the major metabolite for all mutants being N-demethylated noscapine. The highest observed regioselectivity for N-demethylation was 88%. Two hydroxylated metabolites, a catechol and two C-C cleavage products were also detected. P450-mediated production of hydroxylated and N-demethylated noscapine structures may be useful for the development of noscapine analogues with improved biological activity. The variation in substrate turnover, coupling efficiency and product distribution between the active mutants was considered alongside in silico docking experiments to gain insight into structural and functional effects of the introduced mutations. Selected mutants were identified as targets for further mutagenesis to improve activity and when coupled with an optimised process may provide a route for the preparative-scale production of noscapine metabolites.

The electrochemical regeneration of granular activated carbons: A review.

The electrochemical treatment of exhausted granular activated carbon (GAC) has been identified as an effective alternative to traditional adsorbent regeneration methods (e.g. thermal, chemical, and microbial). However, despite its proven potential and initial investigation over two decades ago, the development of this technology has been progressing slowly, hindering its deployment in industrial applications. Thus, a review has been conducted that aims to present the fundamentals of GAC electrochemical regenerative methods, what research has been conducted to develop the technology to the present day, and lastly, identify limitations and future prospects associated with electrochemical methods. The regenerative mechanism is firstly discussed, followed by a presentation of the varying reactor configurations and operating parameters utilized during the electrochemical treatment of GAC materials exhausted with a broad range of wastewater contaminants. Finally, emerging electrochemical technologies used for the commercial treatment of exhausted adsorbent materials and contaminated soils are discussed.

Biocompatible Porous Polyester-Ether Hydrogel Scaffolds with Cross-Linker Mediated Biodegradation and Mechanical Properties for Tissue Augmentation.

Porous polyester-ether hydrogel scaffolds (PEHs) were fabricated using acid chloride/alcohol chemistry and a salt templating approach. The PEHs were produced from readily available and cheap commercial reagents via the reaction of hydroxyl terminated poly(ethylene glycol) (PEG) derivatives with sebacoyl, succinyl, or trimesoyl chloride to afford ester cross-links between the PEG chains. Through variation of the acid chloride cross-linkers used in the synthesis and the incorporation of a hydrophobic modifier (poly(caprolactone) (PCL)), it was possible to tune the degradation rates and mechanical properties of the resulting hydrogels. Several of the hydrogel formulations displayed exceptional mechanical properties, remaining elastic without fracture at compressive strains of up to 80%, whilst still displaying degradation over a period of weeks to months. A subcutaneous rat model was used to study the scaffolds in vivo and revealed that the PEHs were infiltrated with well vascularised tissue within two weeks and had undergone significant degradation in 16 weeks without any signs of toxicity. Histological evaluation for immune responses revealed that the PEHs incite only a minor inflammatory response that is reduced over 16 weeks with no evidence of adverse effects.

Liquid marble formation and solvent vapor treatment of the biodegradable polymers polylactic acid and polycaprolactone.

Liquid Marbles were produced by rolling aqueous droplets on a powder bed of biodegradable polymers, namely polylactic acid (PLA), polycaprolactone (PCL) and blends of these. Solvent vapor treatment was subsequently applied with dichloromethane (DCM). This treatment aligned the polymer chains in order to form a smooth polymeric shell with enhanced mechanical and barrier properties. Whilst a wide range of potential applications for Liquid Marbles exists, the aim here is to encapsulate a solution containing a fertilizer, i.e. urea to produce a controlled release fertilizer. The influences of droplet volume, polymer particle size and solvent vapor treatment time on the liquid marble properties were investigated. Crystallinity and thermal properties were analyzed by differential scanning calorimetry (DSC), surface characteristics and shell thickness by scanning electron microscopy (SEM), mechanical strength and elasticity by compression tests and evaporation rates by thermogravimetric analysis (TGA).

Permeable bio-reactive barriers to address petroleum hydrocarbon contamination at subantarctic Macquarie Island.

A reliance on diesel generated power and a history of imperfect fuel management have created a legacy of petroleum hydrocarbon contamination at subantarctic Macquarie Island. Increasing environmental awareness and advances in contaminant characterisation and remediation technology have fostered an impetus to reduce the environmental risk associated with legacy sites. A funnel and gate permeable bio-reactive barrier (PRB) was installed in 2014 to address the migration of Special Antarctic Blend diesel from a spill that occurred in 2002, as well as older spills and residual contaminants in the soil at the Main Power House. The PRB gate comprised of granular activated carbon and natural clinoptilolite zeolite. Petroleum hydrocarbons migrating in the soil water were successfully captured on the reactive materials, with concentrations at the outflow of the barrier recorded as being below reporting limits. The nutrient and iron concentrations delivered to the barrier demonstrated high temporal variability with significant iron precipitation observed across the bed. The surface of the granular activated carbon was largely free from cell attachment while natural zeolite demonstrated patchy biofilm formation after 15 months following PRB installation. This study illustrates the importance of informed material selection at field scale to ensure that adsorption and biodegradation processes are utilised to manage the environmental risk associated with petroleum hydrocarbon spills. This study reports the first installation of a permeable bio-reactive barrier in the subantarctic.

A permeable reactive barrier (PRB) media sequence for the remediation of heavy metal and hydrocarbon contaminated water: A field assessment at Casey Station, Antarctica.

A field trial was conducted at Casey Station, Antarctica to assess the suitability of a permeable reactive barrier (PRB) media sequence for the remediation of sites containing both hydrocarbon and heavy metal contamination. An existing PRB was modified to assess a sequence consisting of three sections: (i) Nutrient release/hydrocarbon sorption using ZeoPro™ and granular activated carbon; (ii) Phosphorus and heavy metal capture by granular iron and sand; (iii) Nutrient and excess iron capture by zeolite. The media sequence achieved a greater phosphorus removal capacity than previous Antarctic PRB configurations installed on site. Phosphorus concentrations were reduced during flow through the iron/sand section and iron concentrations were reduced within the zeolite section. However, non-ideal flow was detected during a tracer test and supported by analysis of media and liquid samples from the second summer of operation. Results indicate that the PRB media sequence trialled might be appropriate for other locations, especially less environmentally challenging contaminated sites.

The specific reactive surface area of granular zero-valent iron in metal contaminant removal: Column experiments and modelling.

A series of dynamic-flow kinetic experiments were conducted to assess the removal rates of aqueous Cu(2+) and Zn(2+) ions by zero-valent iron (ZVI), a promising material for inclusion in cold-climate remediation applications. The influence of experimental parameters on contaminant removal rates, including aqueous flow rate, operating temperature, and the concentrations of ZVI, salt and dissolved oxygen, was investigated. A mass transport model has been developed that accounts (i) aqueous-phase dispersion processes, (ii) film diffusion of contaminant ions to the reactive ZVI surface and (iii) the reactive removal mechanism itself. Regression to the experimental data indicated that when oxygen is present in the solution feed Cu(2+) and Zn(2+) removal processes were limited by film diffusion. In de-aerated solutions film diffusion still controls Cu(2+) removal but a first-order surface reaction provides a better model for Zn(2+) kinetics. Using air as the equilibrium feed gas, the reactive proportion of the total surface area for contaminant removal was calculated to be 97% and 64% of the active spherically-assumed geometric area associated with ZVI media for Cu(2+) and Zn(2+), respectively. Relative to a gas absorption area, determined in previous studies, the reactive proportion is less than 0.41% of the unreacted ZVI total surface area. These findings suggest that only part of the iron oxyhydroxide surface is reacting during ZVI based metal contaminant removal.

Biodegradable and biocompatible poly(ethylene glycol)-based hydrogel films for the regeneration of corneal endothelium.

Corneal endothelial cells (CECs) are responsible for maintaining the transparency of the human cornea. Loss of CECs results in blindness, requiring corneal transplantation. In this study, fabrication of biocompatible and biodegradable poly(ethylene glycol) (PEG)-based hydrogel films (PHFs) for the regeneration and transplantation of CECs is described. The 50-µm thin hydrogel films have similar or greater tensile strengths to human corneal tissue. Light transmission studies reveal that the films are >98% optically transparent, while in vitro degradation studies demonstrate their biodegradation characteristics. Cell culture studies demonstrate the regeneration of sheep corneal endothelium on the PHFs. Although sheep CECs do not regenerate in vivo, these cells proliferate on the films with natural morphology and become 100% confluent within 7 d. Implantation of the PHFs into live sheep corneas demonstrates the robustness of the films for surgical purposes. Regular slit lamp examinations and histology of the cornea after 28 d following surgery reveal minimal inflammatory responses and no toxicity, indicating that the films are benign. The results of this study suggest that PHFs are excellent candidates as platforms for the regeneration and transplantation of CECs as a result of their favorable biocompatibility, degradability, mechanical, and optical properties.