Ocean alkalinity enhancement (OAE) has emerged as a promising strategy to mitigate ocean acidification and reduce global warming. Traditional metal (e.g., critical materials) mining industries release alkaline waste via mining tailings with high concentrations (99.2%) of calcium and magnesium oxide (CaO, MgO). Incorporating mining waste into OAE processes is less energy intensive than processes relying on calcination of limestone for CaO production. The solubility limit of simulated mining waste in American Society for Testing and Materials (ASTM) seawater is 75 mg center dot L-1, which can sequester 118 mg of carbon dioxide (CO2). The solubility in seawater retrieved from Sunset Beach, FL was 25 mg center dot L-1. Changes in pH, total alkalinity, and total inorganic carbon were analyzed to confirm the successful addition of simulated alkaline mining waste without the formation of secondary precipitation. This study proposes a new OAE strategy where a facility is developed nearby ocean waters that mixes alkaline waste with seawater. Subsequently, the seawater is met with previously captured, pure CO2 to bring the pH back to 8.2 and eliminate the risks of pH shock and secondary precipitation. Technoeconomic analysis estimated an energy requirement of 1.4 GJ per ton of CO2 stored that resulted in a processing cost of $266 per ton of CO2 sequestered (4.2 GJ per ton, $807 per ton of CO2 for real seawater). Results from this study underscore the potential for utilizing mining waste in OAE processes and provide a pathway for practical deployment.

As part of the growing suite of technologies aimed at combatting rising temperatures, negative emissions technologies have become a powerful tool in the global effort to minimize the consequences of human-induced climate change. Among these, carbon removal from aqueous sources, which contain much higher carbon concentrations than the atmosphere, remains largely unexplored. Indeed, developing robust and efficient carbon capture materials for usage in complex aqueous environments remains a significant challenge. Here, we explore the potential of functionalizing polyvinylidene fluoride (PVDF) hollow fiber contactors grafted with a guanidinium-derived polymer sorbent for carbon removal from aqueous sources, including saline waters. Computational screening against amine-based analogs is utilized to identify guanidinium as a promising motif for bicarbonate (HCO3 -) ions binding. To leverage this finding, synthesis of a guanidinium polymer and subsequent covalent grafting onto PVDF hollow fibers is employed to structured polymer-sorbent-grafted hollow fiber contactors. Our prototype achieves an initial HCO3 - removal of 34% with an increase to 98% after four cycles. The functionalized fibers demonstrate aqueous stability over 13 adsorption/desorption cycles in model NaHCO3 solutions where regeneration is facilitated by a mild pH swing. Importantly, the system maintains selective performance in the presence of competitive chloride ions over multiple cycles; carbon removal remained above 10% even at high (10:1) NaCl/NaHCO3 ratios. These findings demonstrate the feasibility of sorbent-based aqueous carbon removal and highlight its potential as a promising approach for negative emissions.

Rare earth elements (REEs) are essential for advanced technologies and yet face significant supply chain risks due to their concentrated global production and limited domestic availability. Addressing this challenge requires efficient processes capable of upgrading low-grade secondary resources such as mine tailings. In this study, we developed a novel separation flowsheet that integrates sequential leaching and 2-stage solvent extraction (SX) processes to recover high-purity heavy REEs (HREEs) and light REEs (LREEs) from a simulated mine-tailing concentrate containing 2.4 wt% total REEs (TREEs; 0.6 wt% LREEs and 1.8 wt% HREEs). Sequential leaching with controlled pH adjustment selectively precipitated REEs while retaining the large amount of impurities in the solution, producing an REE-enriched leachate by following leaching processes with roughly twice the REE concentration and half the impurity concentration compared to that of single-step leaching. The optimized SX flowsheet employed Cyanex 572 to extract HREEs and Fe over LREEs, followed by Fe removal using tributyl phosphate (TBP), while the raffinate stream was processed by SX with di(2-ethylhexyl)phosphoric acid (D2EHPA) to recover LREEs under optimized conditions balancing both extraction efficiency and purity. Although increased extractant availability in the organic phase improved LREE recovery, it also increased co-extraction of Ca, underscoring trade-offs in process optimization. Both HREE- and LREE-rich solutions were subsequently precipitated into solid products via oxalate precipitation, resulting in high-purity REE solids containing similar to 92.0 wt% HREEs (similar to 95.7 wt% TREEs) and similar to 92.8 wt% LREEs (similar to 94.0 wt% TREEs). This proof-of-concept study using simulated mine tailings demonstrates a promising approach for upgrading low-grade REE resources, while highlighting the need for future validation with real materials.

This study aims to understand the effects of system process parameters such as flow rate, adsorbent particle size, and use of recycled adsorbent on denitrogenation performance of a model fuel using mesoporous silica gel. The goal is to reduce the nitrogen content of the model fuel from 1500 parts per million to single-digit ppm to meet ASTM specifications for drop-in fuels. This work was done with the intent of applying adsorptive denitrogenation to sustainable aviation fuel (SAF) product fractions produced via hydrothermal liquefaction (HTL). The adsorption performance of the silica is evaluated via packed column breakthrough data, with data generated from collecting from the column outlet and quantifying nitrogen content via gas chromatography. Select experiments use a significantly larger (2.5x column diameter and length) column to demonstrate linear scalability of the process. Thermogravimetric analysis data is collected to evaluate the effects of thermal calcination as a sorbent regeneration method. Effects of a more complex feed are also investigated using a known reference fuel with additional added nitrogen containing compounds. The results presented in this work successfully demonstrate up to 99.8 % removal of NCCs from a model fuel fraction at an original NCC concentration of approximately 1500 ppm to single-digit parts per million after treatment. We also examine calcination of sorbent materials to remove the adsorbed species to enable sorbent reuse and minimize waste generation and show that the calcined material can be reused up to 5 cycles with reduced adsorption capacity. Overall, this work indicates that adsorptive denitrogenation using silica gel is a viable solution to enable the integration of HTL-derived aviation fuels into existing fuel infrastructure.

Solvent-based absorption systems have emerged in the carbon capture space due to their high absorption capacities, reusability, and favorable energy requirements. Utilizing diethyl sebacate as a solvent for pre- and post-combustion carbon capture has advantages over other solvents, including high hydrophobicity, low viscosity, low vapor pressure, high CO2 solubility, high CO2 selectivity, and being commercially available in large quantities. Despite these advantageous properties, the use of diethyl sebacate as a solvent for post-combustion carbon capture has not been studied in detail. To examine the capability of diethyl sebacate, a scalable, energy-efficient, hollow fiber membrane (microporous polypropylene and polyvinylidene fluoride) contactor (HFMC)-based process with low-cost and high surface area is investigated. A purity of 95.3 % CO2 with 46 % recovery in one absorption stage was achieved, with a permeate flux over one magnitude greater than using a deep eutectic solvent in the same system. Technoeconomic analysis determined a similar to 0.8 GJ per ton of CO2 at a processing cost of similar to$93 per ton of CO2. Results from this work underscore the potential for utilizing green solvents in HFMC-based separation processes for effective carbon capture and provide a pathway towards practical deployment.

Greenhouse gas contributions to climate change have driven intense interest in the separation of CO2 from wet flue gas streams. Deep eutectic solvents (DESs) are an emerging class of highly selective CO2 absorbents. A prototypical DES, reline, is a mixture of choline chloride and urea. Reline is a thermally stable, nontoxic, and biodegradable solvent with negligible volatility and is inexpensive. We demonstrate a scalable and energy-efficient hollow fiber membrane contactor (HFMC)-based process using a green solvent for CO2 capture. This process uses reline in HFMC to provide close interfacial interactions and contact between DES and CO2. This approach overcomes the disadvantages associated with direct absorption in DES and could potentially be applied to a variety of solvent-based CO2 capture methods. Commercial, low-cost polymer hollow fiber membranes were evaluated for the capture of CO2 with reline. From a mixed gas containing N2 and CO2, the DES-based HFMC separated CO2 with a purity of 97 mol %. The effect of the viscosity of reline on the CO2 capture performance was investigated by adding water to the reline. The addition of water to reline significantly reduced its viscosity, which led to a permeate flux of 170 mmol/(m2·h) at 35 °C, 4 bar, and 60 wt % water in solvent, which was approximately 8 times higher than that of the pure reline in the membrane contactor system. In situ Fourier transform infrared spectroscopy and nuclear magnetic resonance (NMR) revealed that reline absorbs CO2 by physical absorption without forming new chemical compounds and that CO2 separation by reline occurs via the pressure swing mechanism. This research provides fundamental insights about green physical solvent-based separation processes and a pathway toward industrial deployment.

Deep eutectic solvents such as reline are an emerging class of low-cost, environmentally friendly solvents with tunable properties that are potentially applicable for the capture and separation of CO2. Experimental measurements showed that a reline-based membrane contactor can capture and separate CO2 via physisorption through a dissolution process with 96.7% purity from a mixed gas containing CO2 and N2 (50:50% molar ratio). We examine the nature of the interaction of CO2 and N2 with reline employing quantum chemical methods. We focus on explaining the mechanism by which CO2 and N2 bind to reline and the reason for the high selectivity for absorption of CO2 compared to N2. We analyze the dynamics, energetics, and binding motifs for CO2 and N2 in reline employing density functional theory, density functional tight binding, and ab initio molecular dynamics. We also investigate the effect of reline on the vibrational spectra of CO2 and reline. Our simulations indicate that the selective capture of CO2 from the mixture of CO2 and N2 is due to the interplay between attractive electrostatic and charge polarization forces with opposing entropic effects, which shift the energetic balance and make the N2 absorption unfavorable in reline.

We demonstrate a scalable and energy-efficient hollow fiber membrane contactor (HFMC)-based process using a green solvent for CO2 capture. This process uses a deep eutectic solvent (DES) in an HFMC to provide close interfacial interactions and contact between the DES and CO2. This approach overcomes disadvantages associated with direct absorption in DES and could potentially be applied to a variety of solvent-based CO2 capture methods. Commercial low-cost polymer hollow fiber membranes (e.g., microporous polypropylene) were evaluated for CO2 capture with reline, a prototypical DES. Single-gas measurements showed that the DES-based polypropylene HFMC can capture and separate CO2 while rejecting N2. From a mixed gas containing 50 mol % N2 and 50 mol % CO2, the DES-based HFMC separated CO2 with a purity of 96.9 mol %. The effect of several process parameters including solvent flow rate, pressure, and temperature on the CO2 separation performance was studied. The flux of the recovered CO2 was 67.43 mmole/m2/h at a feed pressure of 4 bar. In situ Fourier transform infrared (FTIR) measurements combined with density functional theory (DFT)-based molecular dynamics simulations revealed that reline absorbs CO2 by physical absorption without forming a new chemical compound, and CO2 separation by reline occurs via the pressure swing mechanism. This research provides fundamental insights about physical solvent-based separation processes and a pathway toward practical deployment.

Membrane solvent extraction provides an energy -efficient and environmentally friendly process to recover rare earth elements from electronic waste.

In recent years, solar energy-driven photocatalysis materials have drawn significant attention to addressing the global energy and environmental crisis. However, many of the semiconductor photocatalysts are unable to absorb the visible light of the solar spectra due to their wide band gap. The incorporation of a foreign element such as a dopant in the lattice of these photocatalysts was shown to reduce their band gap and enhance visible light absorption. The doping of semiconductors can be performed using several techniques such as sol-gel, hydrothermal, solvothermal, and plasma-based doping. However, plasma-based doping has been considered a highly efficient approach due to the reduction of the band gap to a large extent, enhancement of visible light absorption, and remarkable photocatalytic activities under visible light illumination. The plasma-based doping approach offered many advantages such as high reactivity, process simplicity, scalability, energy efficiency, homogeneous doping, no chemical inventory, low pressure, and low-temperature operation, and flexibility of operation under gas and liquid phase media. Further advancement of plasma-based doping can be achieved through more theoretical studies allowing an in-depth understanding of the mechanisms and interactions of the species involved. This will facilitate the synthesis and application of doped photocatalysts in a cost-effective manner. This review surveyed recent advances in a wide range of semiconductor photocatalysts doped with various dopants using plasma treatment. Various plasma methods for doping semiconductor photocatalysts and their fundamental mechanisms were discussed. The performance characteristics of the plasma-doped photo-catalysts were compared to other methods in terms of energy and environmental applications including degra-dation of environmental contaminants and solar fuel production such as hydrogen production from water splitting using visible light-driven solar energy. Finally, potential future research directions were recommended for the applications of the efficient photocatalysts developed by plasma treatment.

Heterogeneous photocatalysis is considered to be a sustainable solution for treating organic pollutants in wastewater. Tin oxide (SnO2) has received immense attention from researchers due to its excellent photocatalytic activity, low cost, thermal stability, and resistance to photo erosion. The structural properties of SnO2, different strategies for doping of SnO2, organic degradation mechanisms, and optimization of operational parameters for enhanced photocatalysis were critically analyzed. Photocatalytic activity of pristine SnO2 was enhanced by doping with metal oxide-based semiconductor materials, metals (transitional and earth), and non-metals. Doped SnO2 exhibits higher photocatalytic efficiency than pristine SnO2 due to the enhanced charge carrier separation, reduced electron-hole pair recombination, higher surface area, and lower band-gap energy. Green synthesized TiO2 doped SnO2 exhibited reduced band gap energy of 2.8 eV, and degraded 96 % MB within 75 min under visible light irradiation. The lowest bandgap energy for transitional metal-doped SnO2 was achieved by Mn-doping on SnO2 with a bandgap of-2.48 eV, whereas Cu-SnO2 and pure SnO2 have bandgap energies of 3.67 eV and-3.75 eV, respectively. Copper chromite spinel nanoparticles (CuCr2O4) doped SnO2 with a band gap energy of 1.39 eV degraded crystal violet (CV) dye completely at neutral pH. Gadolinium (Gd) doped SnO2 particles showed the highest surface area (58 m2/g) which was almost double the pristine SnO2 particles. The degradation of organic dyes by doped-SnO2 depended on initial pH, catalyst dosage, pollutants concentration, dose, light intensity, etc. For the degradation of cationic dye (MB), approximately 50 % more degradation was found at basic pH than at acidic pH utilizing pristine SnO2 nanoparticles. On the contrary, about 20 % more degradation was found for anionic dye (Congo Red) degradation at acidic pH compared to basic pH. Moreover, optimization of catalyst dosage can result in about 50 % more degradation of pollutants. The ZnS-doped SnO2 photocatalysts have shown an increased rate constant of photocatalytic reaction by 24.5 times when the con-centration was reduced from 30 mg/L to 5 mg/L. This review also assessed the future research directions to develop sustainable organic pollutants-based wastewater using SnO2.

This study investigated a novel membrane solvent extraction (MSX) process for the recovery and separation of lithium (Li) from clay minerals using a cation exchange organic extractant [di-(2-ethylhexyl)phosphoric acid] (DEHPA). The Li is selectively extracted from clay mineral leachate solution using highly efficient aluminum hydroxide sorbents to form lithium aluminum double hydroxide sulfate (LDH sulfate) as the precipitate. Several delithiation methods have been explored to separate Li from aluminum (Al). LDH sulfate is dissolved in dilute H2SO4 and used as the feed solution, and DEHPA is used to selectively separate Li and Al from the feed solution. The MSX process immobilizes DEHPA in the microporous membrane pores and continuously removes Al from the feed solution to obtain pure Li. The efficiency of DEHPA for the selective separation of Li from Al is determined by measuring its distribution coefficient. This study used the optimum feed solution pH of 3, strip solution concentration of 2 mol/L H2SO4, and an organic phase composition of 30% v/v DEHPA in Isopar-L. The MSX process achieved a Li yield of about 92% and a purity of ⩾ 94%. The results suggest that the innovative MSX technology is a time- and energy-efficient approach for the recovery and separation of high-purity Li for application in Li-ion batteries and other clean energy technologies.

We report on observations of strong degradation of a polycarbonate vessel by a solvent being considered for a CO2 capture process, diethyl sebacate. This degradation led to failure of a polymeric hollow fiber membrane unit. Additional tests showed rapid degradation of polycarbonate safety glasses and polystyrene-based petri dishes by exposure to diethyl sebacate at ambient conditions. We also report on safe operations with diethyl sebacate in extensive experiments studying the corrosion of steel in CO2-pressurized reactors lined with PTFE and using PTFE gaskets. Used diethyl sebacate was also stored for long time periods in bottles made from low-density polyethylene bottles without physical deterioration. These observations indicate that care must be taken in development of new contactors and processes for CO2 capture with diethyl sebacate and related solvents and in the choice of material for storage.

The breakdown characteristics of SF 6 /CO 2 /O 2 and SF 6 /N 2 /O 2 ternary gas mixtures were investigated with AC test voltages under both slightly uniform and non-uniform electric fields. In this study, the slightly uniform field represented by a sphere-plane electrode, while a rod-plane electrode configuration provided the non-uniform field. The gap lengths between the electrode varied from 5 mm to 25 mm, and the gas pressure was fixed at 1.0 bar (abs). The tests were measured at various mixing ratios considering a small percentage of O 2 in each gas mixture. The effects of additional O 2 in SF 6 /CO 2 and SF 6 /N 2 on the breakdown voltages were discussed to obtain a reasonable mixing ratio of the ternary gas while maintaining the insulation properties of the gas. The addition of 10% O 2 in the SF 6 /CO 2 mixture showed a significant increase in the breakdown voltage for all gap distances under both electrode configurations. Meanwhile, only 5% of O 2 is required to increase the breakdown voltage in the SF 6 /N 2 mixture under the rod-plane electrode, and 10% of O 2 is required to be added for the sphere-plane configuration. Apart from the experimental work, this paper also discusses a simulation study on the maximum electric field for each breakdown test. It is found that the rod-plane electrode provides a higher electric field compared to the sphere-plane electrode configuration.

Photovoltaic (PV) cleaning systems are getting popular to clean their dusty and sticky surface developed by foreign particles with morning dew and light rain. However, a non-automated PV cleaning system requires human intervention, time, and cost and is often not feasible for large PV generations. Current studies investigate different types of automated cleaning systems, which are being deployed to overcome such dust problems ranging from wet to dry cleaning. Exposure to different types of automated PV cleaning systems has been shown in other studies to be related to adverse effects in overcoming dust problems. Such approaches, however, have failed to address the sticky layer of dust and foreign particles accumulated on PV surfaces. This paper presents the development of a time-based PV cleaning brush controller that is operated through an automatic periodical time activation method. This study focuses on the mechanical design of the brush controller encompasses two carrier and one rotating motors, nylon brush in aluminum structured frame, hollow aluminum shaft, linear rails, real time clock (DS1307), and Arduino Uno microcontroller. A self-designed small-scale test-bed of 100W PV module was installed on a rooftop of a room within the premises of Universiti Tun Hussein Onn Malaysia (UTHM), Johor, Malaysia. The functional time-based cleaning brush controller was configured to operate at a frequency of five cleaning cycles per day without human intervention within the test-bed. It is a dry cleaning approach without any soapy water employment to realize the multiple cleaning cycles every day at 7A.M. within the overall testing. Results indicate that dust accumulation has a substantial effect on the PV performance on a timescale of seasons in this location. In addition, the system achieved a 72% of dust removal rate from the 5 cycles, whilst it is 80.6% at its 10 cycles of cleaning. Overall, the result shows that the energy yield of PV with the cleaning system is enhanced by 26% more than that of the unclean PV. The cleaning system design can be very effective for rooftop-based PV applications, as recently, there are about 6.8MW rooftop based net energy metering project planted at UTHM, a way to support green energy growth under sustainable development goals.