Gas Removal Research Articles

Carbon footprint of t-shirts made of cotton, polyester or viscose

Carbon footprint (CFP) is an effective tool for calculating and assessing greenhouse gas (GHG) emissions and removals in a product life cycle using a single impact category of climate change. This study performed the CFP calculation and assessment for cotton t-shirt, polyester t-shirt and viscose t-shirt, complying with the system boundary from raw material extraction phase to end-of-life. Results demonstrated that yarn manufacturing contributes most of the CFP (36.1%-50.5%), followed by the product use phase (30.6%-48.3%) and fabric manufacture phase (19.6%-20.3%). Energy consumption is the main contributor to CFP in production processes. Additionally, the carbon sequestration effect of plant-derived fibres such as cotton and viscose played an important role to offset GHG emissions in the life cycle of t-shirts. The effect of carbon sequestration is more significant with the increase of product service life. Findings of this study can provide carbon emission reduction references for enterprises and consumers. In order to reduce the CFP in the entire life cycle of t-shirts, it was recommended that enterprises need to innovate production technology and increase the proportion of renewables in energy structures to replace the use of fossil energy, and consumers prolong the life cycle of products.

Досвід проєктування та впровадження системи індивідуального регулювання тиску в камері коксування.

The purpose of this article is to show the possibility of using the GIPRO system, designed for individual pressure regulation in each coking chamber, on existing and new coking batteries. The prerequisites for the emergence of the technology of individual pressure regulation are described. The basics of processes occurring in coking chambers, which lead to undesirable environmental and production consequences, are explained. These negative effects can be leveled with the use of PROven® and SORRESO individual regulation systems developed in the world. The article provides a comparative analysis of various systems of individual pressure regulation, which are used in world practice, and the system of maintaining individual pressure in the coking chamber - the GIPRO system, developed by SE "GIPROKOKS" - with other existing global analogues. The history of the introduction of various systems of individual pressure regulation in the world is briefly presented. Design features of the systems themselves are described. The path of development of the "GIPRO" system from the idea to the experimental installation is described. The results of the design and installation of the "GIPRO" system at some factories in China and India are given. A description of the "GIPRO" system during operation with negative pressure in the gas tank is given, as well as other possible modes of operation of the system are presented. On the example of the developed projects, the possibility of using the "GIPRO" system for installation, both on large-capacity coke batteries with tamping technology that are being built, and on the local modernization of gas removal equipment on existing coke batteries, has been proven. Conclusions were made about the possibility and expediency of using the developed system for coke batteries of various designs. The developed system can be used to improve the environmental performance of existing coke batteries. Installation of the system on a working coke battery can be implemented with minimal loss of coke production on that battery. Keywords: hard coal, coking chamber, system of individual pressure regulation, reduction of harmful emissions, experimental installation, riser valve box. Corresponding author M.O. Solovjov, e-mail: solovjov.gpk.ua@gmail.com

Impact of rectal gas on the planning target volume margin for pelvic bone and prostate matching in prostate cancer patients receiving volumetric-modulated arc therapy.

We performed daily cone-beam computed tomography (CBCT) to determine the impact of rectal gas on the movements of prostate and seminal vesicles (SVs). We aimed to determine the relationship between planning target volume (PTV) margins and rectal gas. In 30 treatments of 15 prostate cancer patients, excessive rectal gas was removed and CBCT images were analyzed. Image registration between planning CT and daily CBCT images before and after rectal gas removal was performed for pelvic bone and prostate matching. The couch movement distance between each matching was considered the prostate movement. In addition, we measured SV tip movement between each matching. The anterior-posterior movement of the prostate before rectal gas removal (3.1 ± 2.9 mm) was significantly greater than that after rectal gas removal (1.2 ± 1.2 mm; p < 0.01). The left-right and superior-inferior movements were similar regardless of the presence or absence of rectal gas. The SV movement distances before and after rectal gas removal were 11.0 ± 5.8 mm and 4.6 ± 3.8 mm, respectively (p < 0.01), in pelvic bone matching, and 8.0 ± 4.2 mm and 3.8 ± 3.2 mm, respectively (p < 0.01), in prostate matching. After rectal gas removal, the SV position did not differ significantly between each matching. In 26 of the 30 treatments, SV movement distance in the presence of rectal gas was >6 mm, which is the minimum PTV margin at our institution. In comparison, after rectal gas removal and prostate matching, only 6 treatments demonstrated an SV movement distance of >6 mm. In the presence of rectal gas, the SVs require greater PTV margins than the prostate. Rectal gas removal should be considered if the movement distance on prostate matching is greater than the minimum PTV margin at treating institution.

Performance analysis of the acid gas removal from syngas based on self-heat recuperation technology

Considering the high energy consumption of the acid gas removal (AGR) unit in integrated gasification combined cycle (IGCC) systems, this paper innovatively combines the two self-heat recuperation technology (SHRT) forms with the syngas purification process. The AGR unit and the power generation unit in this paper are simulated by Hysys V11. By establishing the energy balance and exergy balance equation for each component, the change of energy consumption and exergy loss of the unit before and after the process modification is analyzed. Compared with the two improved methods, Case1 uses low-pressure water as the working medium of SHRT process, which has the characteristics of high COP of heat pump and low throttling loss, and achieves good results in terms of operating cost and exergy loss. Case1 has 3.75% lower operating cost compared with the basic process, the annual operating cost of H2S removal is reduced by 144,200$, and the exergy loss of the AGR unit is reduced by 23.48 kW. Case2 does not have advantages under the two evaluation indexes. Subsequently, sensitivity analysis of the inlet pressure of Case1 heat pump exchanger further improves the energy-saving potential of this retrofit solution. The article explains the effect of the SHRT process in the AGR unit on the exergy loss of the rich solvent regeneration process and the distillate cooling process, and verifies the energy-saving potential of the SHRT in the acid gas removal unit of IGCC.

Toxic gas removal with kaolinite, metakaolinite, radiolarite, and diatomite

In this study, some clays and dead microorganisms were compared in terms of their adsorption ability against special toxic gases. To this end, an experimental investigation was conducted to explore the adsorption kinetics of kaolinite, metakaolinite, radiolarite, and diatomite to ammonia (NH3), ethylene (C2H4), and carbon dioxide (CO2). Numerous analyses, such as x-ray fluorescence (XRF), x-ray diffraction (XRD), thermo-gravimetric analysis (TGA), scanning electron microscopy (SEM), and particle size distribution, have been performed for mineralogical and structural characterization of studied materials. Also, adsorption characteristics were investigated with the help of an ultra-precision scale and computer-controlled multi-gas control system. Since ammonia has the highest dipole moment among all studied gases, its removal efficiency was found as the highest in all materials. Regarding clay substances, metakaolinite indicated a lower response than kaolinite due to phase transformation. But, considering the microorganisms, diatomite toxic gas uptake is at least five times better than examined clays while the gas uptake behavior of radiolarite is analog to metakaolinite. Moreover, the adsorption behaviors of proposed materials are clarified with Langmuir isotherms, The results could facilitate improvements in applying microorganisms to the toxic gas environment as a natural adsorbent material.

Criteria of thermochemical conditions of steam gas explosions in dynamic accident modes at nuclear power units with WWER reactors

The main lessons of the major accident at the Fukushima-Daiichi NPP in 2011 for the nuclear power industry identify the need to model, analyze and develop emergency measures for relatively unlikely events with catastrophic environmental consequences, taking into account multiple failures of safety systems. Steam-gas explosions became one of the main causes of the catastrophic environmental consequences of the Chernobyl and Fukushima accidents. Criteria and conditions for the occurrence of steam-gas explosions in dynamic emergency modes in the "tight" reactor circuit of nuclear power reactor units (NPP) with water-water reactors (WWER) with failures of safety systems valves and emergency steam gas removal are determined by the rate of change of thermodynamic and physico-chemical parameters. A method for determining the criteria and conditions for the occurrence of steam-gas explosions in dynamic accident modes with a "tight" reactor circuit and failure of safety valves for modeling the initial emergency events – seismic effects, falling of massive objects, etc. is presented. The conditions for the occurrence of hydrogen explosions are determined by the maximum rate of increase in the temperature of fuel oil shells, and the conditions for steam explosions are determined by the maximum rate of pressure increase as a result of the intensification of vaporization processes. The criteria for the occurrence of steam explosions in dynamic emergency modes are determined by the maximum pressure amplitude and the propagation speed of acoustic disturbances in the steam volume. And the criteria for hydrogen detonation in dynamic emergency modes are determined by the maximum amplitude of the increase in the temperature of the fuel shells and the average flow rate of the coolant in the active zone of the reactor.

The Permeation of High Concentration Hydrogen Sulfide (H2S) Gas Using PTFE (Polytetrafluoroethylene) and PVDF (Polyvinylidene Fluoride) membranes

Hydrogen sulfide (H2S) is a toxic, corrosive, and flammable gas. The presence of H2S gas can be reduced by a permeation method using PTFE (Polytetrafluoroethylene) membranes and PVDF (polyvinylidene fluoride) membranes. This H2S gas passed through the membrane and was then captured by the SAOB (Sulfide Anhydride Oxidant Buffer) in S2- species form. A visible spectrophotometer was applied for the analysis of passed H2S gas. Using a PTFE membrane, the optimum flow rate was obtained at 14.71 mL/min, with a mass flux of 0.825 kg/m2.hour, permeability coefficient of 0.696 kg/m2.hour.bar, and percent removal of H2S gas was 88.14%. The optimum flow rate for the SAOB was obtained at a rate of 0.30 mL/min with a mass flux of 0.843 kg/m2.hour and a percent removal of H2S gas of 89.98%. Based on the results obtained on the PVDF membrane, the mass flux produced in the optimization of H2S gas is 0.742 kg/cm2.hour, and the optimization of the SAOB solution is 0.754 kg/cm2.hour. The resulting permeability coefficient value is 0.741 kg/cm2.hour. The results indicate that this study can remove H2S gas at the optimum H2S gas flow rate of 4.76 mL/minute of 94.89% and the optimum SAOB flow rate of 0.3 mL/minute of 95.66%

A novel gas removal method for the removal of C2H2 in calcium carbide slag slurry by fine bubbles combined with air purging: performance, mechanism, and in situ bubble imaging analysis

About 60% of carbon emissions in the cement industry come from the decomposition of limestone. As a key low-carbon technology of raw material substitution, calcium carbide slag (CCS, low-carbon calcareous material) can replace limestone to produce cement, desulfurizer, and other products, which can achieve carbon emission reduction and the upcycling of CCS. However, the release of residual C2H2 in CCS brings safety and environmental risks, which seriously restricts the upcycling of CCS. In this study, a novel gas removal method of fine bubbles (FBs) degassing was proposed for the removal of C2H2 in solid CCS particles, and an advanced in situ bubble imaging technology was used to investigate the performance and mechanism of C2H2 removal. The results indicated that approximately 70% of C2H2 (encapsulated C2H2) in CCS was difficult to remove by drying or slurrying. Under the optimal condition, the C2H2 removal efficiency was approximately 61.0%, and the amount of C2H2 released from the CCS slurry decreased by 92.9%. In the process of FBs degassing, large CCS particles in the CCS slurry were broken up into fine particles via the erosion mechanism, thus promoting the reaction of the encapsulated calcium carbide with water to produce C2H2. The generated C2H2 was dissolved in the slurry and could be quickly removed by FBs (<500 μm) with a fast mass transfer rate under the slight negative pressure. This work provides a novel gas removal method for effectively removing C2H2 in CCS and avoiding security and environmental risks, provides technical support for the upcycling of CCS, and provides a reference for the separation of other similar multiphase systems (e.g., gas–liquid/gas–liquid–solid, oil-liquid/oil-liquid–solid).

Technoeconomic Feasibility of Hydrogen Production from Waste Tires with the Control of CO2 Emissions.

The worldwide demand for energy is increasing significantly, and the landfill disposal of waste tires and their stockpiles contributes to huge environmental impacts. Thermochemical recycling of waste tires to produce energy and fuels is an attractive option for reducing waste with the added benefit of meeting energy needs. Hydrogen is a clean fuel that could be produced via the gasification of waste tires followed by syngas processing. In this study, two process models were developed to evaluate the hydrogen production potential from waste tires. Case 1 involves three main processes: the steam gasification of waste tires, water gas shift, and acid gas removal to produce hydrogen. On the other hand, case 2 represents the integration of the waste tire gasification system with the natural gas reforming unit, where the energy from the gasifier-derived syngas can provide sufficient heat to the steam methane reforming (SMR) unit. Both models were also analyzed in terms of syngas compositions, H2 production rate, H2 purity, overall process efficiency, CO2 emissions, and H2 production cost. The results revealed that case 2 produced syngas with a 55% higher heating value, 28% higher H2 production, 7% higher H2 purity, and 26% lower CO2 emissions as compared to case 1. The results showed that case 2 offers 10.4% higher process efficiency and 28.5% lower H2 production costs as compared to case 1. Additionally, the second case has 26% lower CO2-specific emissions than the first, which significantly enhances the process performance in terms of environmental aspects. Overall, the case 2 design has been found to be more efficient and cost-effective compared to the base case design.

Compressing Natural Gas - Carbon Capture - EOR (CAGAR) Innovation: Cost Effective Sustainable Flare Gas Utilization to Boost Oil Production

Drilling natural gas (CNG) is a promising environmentally friendly gasoline substitute. It is produced at a reasonable price. Flaring, on the other hand, emits 300 million tons of CO2 into the environment wasting vital energy resources. As a result, rather than releasing CO2 into the atmosphere, it is used to boost oil production as a CO2 EOR to fulfill global oil demand that continues to rise. To achieve a sustainable oil and gas production by reducing greenhouse gasses (GHG) through flaring reduction innovations comprising gas purification and carbon capture that utilizes the associated gas as a viable compressed natural gas (CNG) and enhanced the oil recovery. Natural gas linked with crude oil (CH4 dominated) is processed in two units. The first one is a gas purification unit where natural gas is purified in compressor, Acid Gas Removal Unit (AGRU), dehydration unit, and hydrocarbon recovery producing viable CNG. In the flaring unit gas is burned converting the CH4 to CO2. Flared gas is captured in a Carbon Capture Storage (CCS). Furthermore, CO2 is centralized in the EOR-System to be injected into the reservoir as CO2-EOR by interacting with oil causing oil to swell and reduce its viscosity leading to oil flow easier through the pores. This research elucidates that CAGAR could produce 2,970 mmbtu/d of CNG. Beside producing profitable products, CAGAR also boosted oil production by adding an extra 21,369.6 bbl/d oil recovery. According to the results, the production of the CAGAR method of flare gas utilization is the most economical technology with an annual sales from oil recovery and CNG of 455,768,373 USD so that CAGAR get a profit before tax of 248,288,632.81 USD and a profit after tax of 207,479,740.57 USD with a parameter calculation is a positive NPV, IRR of 30.26% including the cash flow and present value start to be positive in the 3rd year when the system starts operating. CAGAR has a payback period of 2.7 years. Technical and economic analysis shows there improved oil recovery and improved environmental protection. So it can be concluded that CAGAR has good prospects and deserves to be implemented.

The next climate war? Statecraft, security, and weaponization in the geopolitics of a low-carbon future

The impacts of global climate change on international security and geopolitics could be of historic proportion, challenging those of previous global threats such as nuclear weapons proliferation, the Great Depression, and terrorism. But while the evidence surrounding the security impacts of climate change is fairly well-understood and improving, less is known about the security risks to climate-technology deployment. In this study, we focus on the geopolitical, security, and military risks facing negative emissions and solar geoengineering options. Although controversial, these options could become the future backbone of a low-carbon or net-zero society, given that they avoid the need for coordinated or global action (and can be deployed by a smaller group of actors, even non-state actors), and that they can “buy time” for mitigation and other options to be scaled up. We utilize a large and diverse expert-interview exercise (N = 125) to critically examine the security risks associated with ten negative emission options (or greenhouse gas removal technologies) and ten solar geoengineering options (or solar radiation management technologies). We ask: What geopolitical considerations does deployment give rise to? What particular military applications exist? What risks do these options entail in terms of weaponization, misuse, and miscalculation? We examine such existing and prospective security risks across a novel conceptual framework envisioning their use as (i) diplomatic or military negotiating tools, (ii) objectives for building capacity, control, or deterrence, (iii) targets in ongoing conflicts, and (iv) causes of new conflicts. This enables us to capture a far broader spectrum of security concerns than those which exist in the extant literature and to go well beyond insights derived from climate modelling or game theory by drawing on a novel, rich, and original dataset of expert perceptions.

Efficacious removal of benzene and ammonia gases over visible light irradiated activated carbon

Removal efficiencies of benzene and ammonia were studied using as-received commercial activated carbon (AC) at 0%, 30%, and 60% relative humid (RH) conditions with and without visible light irradiation. We showed that light enhanced the removal efficiency of benzene even under nitrogen, and the enhancement effect became more pronounced in the presence of H2O and O2. We also demonstrated that the ammonia removal efficiency can be enhanced by visible light irradiation under optimum humidity conditions. We further suggested more efficient migration of NH3 through the nanoporous channels of AC facilitated by light and water. Fourier-transform infrared (FT-IR) analyses addressed the changes in surface structure of AC caused by oxidizing agents such as OH. radicals created with light irradiation and other reagents.

In-situ synthesis and assembly of nanospheres (Py1H2PW, Py2H1PW, and Py3PW) in wood to promote flame retardation

Hybrid wood is a composite with the advantages of both wood and inorganic material. Here, a novel hybrid wood was fabricated from wood and nanospheres by the in-situ assembly of phosphotungstic acid (HPW) and pyridine (PY) at room temperature. The uniformly distributed amphiphilic PY-PW nanospheres provided controllable particle size and acid properties by changing the HPW-PY molar. Examination under Scanning electron microscopy (SEM) showed the presence of a uniform nanosphere coating by the nanospheres, and FE-SEM/EDS showed even distribution on the cell walls. The successful synthesis of the nanospheres in the wood was confirmed by Transmission electron microscopy (TEM). The PY-PW/wood hybrid was also resistant to leaching, attributed to the amphiphilicity of the nanospheres. The hybrid wood also showed superior flame retardation, with a UL-94 V-0 rating, and significantly reduced the peak heat release rate (pk-HRR) and total smoke release (TSR) values of the untreated wood by 44.7 % and 51.7 %, respectively. The enhanced flame retardation was attributed to synergistic effects and catalytic carbon reactions resulting from high-density nitrogen/phosphorus/oxygen cross-linking in the carbon layer in the condensed phase and the removal of combustible gases by free radicals. This hybrid wood material has potential application for the development of fire-safe wood.

АДАПТАЦІЯ ПРОЦЕСУ АДИТИВНОГО ВИГОТОВЛЕННЯ МОДЕЛЕЙ ДЛЯ ГАЗИФІКАЦІЇ ЇХ В ПІЩАНІЙ ФОРМІ ПРИ ЗАЛИВАННІ МЕТАЛУ, А ТАКОЖ ДЛЯ УТИЛІЗАЦІЇ ВІДХОДІВ ПІНОПОЛІСТИРОЛУ

The technological method in the field of foundry production is described, which combines additive manufacturing (AM) of disposable foundry polymer patterns with waste polystyrene (EPS) waste disposal. It was created to switch to the method of Lost Foam casting on gasified patterns (LFC), from the current method of casting on printed patterns of fired. The latter method is used because modern printed patterns have a high density and ash content, which degrades the quality of metal castings when used for LFC. EPS disposal gives an environmental effect, and AM patterns are an example of the spread of digitalization and automation of foundry production. Examples of EPS disposal, examples of castings after firing additively manufactured patterns and the ash residue, consisting of carbon, found in the working cavities of molds after firing such patterns are described. Examples of printing patterns with a cellular core and a ventilation channel are shown, an unsuccessful example of aluminum casting by the LFC method in a vacuumed sand mold, as well as an example of a 3D printer for printing using crushed plastic or plastic granules. The developed method of printing one-time foundry patterns for gasification in sand foundry mold corresponds to the trend of spreading AM in foundry production. If the specific weight of the printed pattern is too high, then new LFC methods are used with the removal of excess gases from the gasification of the pattern through the ventilation duct in the pattern and tubular evaporation outside the mold and their oxidation, in particular by our method. Such neutralization of gaseous waste at LFC rightly complements the utilization of EPS solid waste as a raw material for AM foundry patterns, together these methods give a synergistic effect on environmental protection, improving the working conditions of foundries and reducing the cost of cast products while improving its quality. Keywords: Lost Foam casting; gasified patterns; 3D printing; additive manufacturing; one-time patterns; burning patterns; expanded polystyrene; disposal of polymer waste.

Hydrogen Sulfi de Adsorption on Alumina/Graphene Oxide Composites at Ambient Temperature

Hydrogen sulfi de (H2S) is one of the most common pollutants found in natural gas and industrial waste. Over the few decades, the removal of H2S has become a signifi cant problem. In the fi eld of a clean environment such as water purifi cation and toxic gas removal, graphene oxide (GO) has been found to have advantages. In this study, the infl uence of GO on alumina (Al2O3) as an adsorbent of H2S was examined. A series of Al2O3/GO (AGO) composites with varying graphene oxide addition (0.5–3.0 wt%) were prepared using the high-temperature sintering method. The X-ray diffraction patterns indicate the primary phase of Al2O3 with hexagonal crystal structure for all AGO composites. Raman spectrometry measurements confi rmed that the GO particles were incorporated in AGO composites. The TEM image indicated that GO nanosheets were embedded between Al2O3 grains. The effi ciency of AGO adsorbent at ambient temperature was investigated and compared with the pristine Al2O3 adsorbent. The AGO composites adsorbent demonstrated the H2S breakthrough capacity in the range of 0.07–0.43 mg/g, which is higher than that of pristine Al2O3 (0.06 mg/g). Furthermore, the highest H2S breakthrough capacity of 0.43 mg/g was obtained from AGO containing 3.0 wt% GO. This investigation demonstrates that the AGO adsorbent fabricated using a simple method has the potential to be used for H2S removal at ambient temperature.

Acid Gas and Tar Removal from Syngas of Refuse Gasification by Catalytic Reforming

The existence of acid gas and tar in syngas of municipal solid waste gasification limits its downstream utilization as a clean energy source. Here, we investigated the catalytic removal of HCl and tar. The key parameters affecting the catalytic reaction, including space velocity, temperature, the amounts of active metals in the catalyst and the carrier material, were studied, targeting optimized operating conditions for enhanced syngas purification. The morphology, mineral phases, surface area and pore size before and after the reaction were investigated to understand the mechanism to dominate the reaction. The results showed that the removal rate of CaO adsorbent and HCl reached 96% at 400 °C. When the space velocity ratio was 1.0 and the temperature was 400 °C, HCl removal (97%) by NaAlO2 was even better. Nevertheless, clogging was observed for NaAlO2 via the BET test after reaction to jeopardize its durability. A level of 25% Ni doping on Zr1-x(Cex)O2 support provides high stability for tar removal. This is because the Zr1-x(Cex)O2 carrier has higher carbon deposition resistivity than the Al2O3 carrier. The EDX results confirmed that a large amount of C (79.3%) was accumulated on the commercial catalyst surface supported by Al2O3 (25% Ni-based). As for the temperature, a temperature higher than 800 °C could not enhance the efficiency of tar removal, likely due to catalyst deactivation. Carbon deposition and agglomeration are the two main causes of catalyst deactivation. At 800 °C, 25% Ni-based synthetic catalyst can convert 48.5 ± 19.4% tar to low molecular weight organic compounds. By contrast, such a conversion rate under the same temperature only accounted for 5.0 ± 6.8% based on a commercial catalyst. These insights point to the important role of catalyst support materials.

An insight into simultaneous phase transition phenomena and melt-rheology of low-density polyethylene/ethylene–vinyl acetate copolymer/expanded graphite nanocomposites through continuous extrusion foaming process

In the present article, the influences of expanded graphites (EGs) with small, medium, and large aspect ratios (SEG, MEG, and LEG, respectively) on the foamability of low-density polyethylene (LDPE)/ethylene–vinyl acetate copolymer (EVA) blend obtained from continuous extrusion foaming process were studied. The addition of EGs to the PE/EVA blend resulted in foams with smaller cells and higher cell densities. Among the different nanofillers used, EG with larger aspect ratio caused the formation of PE/EVA foams with higher void fraction, smaller cell size and larger cell density. EG nanoplatelets assisted bubble nucleation and acted as an impermeable barrier against the gas removal from the melt, where LEG behaved more successfully due to having a larger surface area with the melt. During the bubble nucleation and growth stages, PE/EVA liquid–liquid and solid–liquid phase separations took place concurrently. The presence of EG nanofillers influenced the PE/EVA phase separation and increased the mutual solubility of the polymeric constituents in each other. Besides, EG nanolayers enhanced the viscoelastic properties of PE/EVA melt, and thus prevented cell wall rupture and gas release from the melt.

Theoretical Investigations on MIL-100(M) (M=Cr, Sc, Fe) with High Adsorption Selectivity for Nitrogen and Carbon Dioxide over Methane.

The removal of impurity gases (N2 , CO2 ) in natural gas is critical to the efficient use of natural gas. In this work, the selective adsorption for N2 and CO2 over CH4 on MIL-100 (M) (M=4 Cr, 10 Cr, 6 Fe, 1 In, 1 Sc, 3 V) is studied by density functional theory (DFT) calculations. The calculated adsorption energy of the large-size cluster model (LC) of MIL-100 (M) shows that the 4 MIL-100 (4 Cr) is the best at the refinement of natural gas due to the lower adsorption energy of CH4 (-2.58 kJ/mol) in comparison with that of N2 (-21.49 kJ/mol) and CO2 (-23.82 kJ/mol). 1 MIL-100 (1 Sc) and 1 MIL-100 (6 Fe) can also achieve selective adsorption and follows the order 4 MIL-100 (4 Cr)>1 MIL-100 (1 Sc)>1 MIL-100 (6 Fe). In the research of the selective adsorption mechanism of MIL-100 (M) (M=4 Cr, 1 Sc, 6 Fe), the independent gradient model (IGM) indicates that these outstanding adsorbents interact with CO2 and N2 mainly through the electrostatic attractive interaction, while the van der Walls interaction dominates in the interaction with CH4. The atomic Projected Density of State (PDOS) further confirms that CH4 contributes least to the intermolecular interaction than that of CO2 and N2 . Through the scrutiny of molecular orbitals, it is found that electrons transfer from the gas molecule to the metal site in the adsorption of CO2 and N2 . Not only does the type of the metallic orbitals, but also the delocalization of the involved orbitals determines the selective adsorption performance of MIL-100. Both Cr and Sc share their orbitals with the gases, making 1 MIL-100 (1 Sc) another potential effective separator for CH4 . Additionally, the comparison of adsorption energy and PDOS shows that the introduction of ligands such as benzene impedes the electron donation from gas molecules (CO2 , N2 ) to the metal site, indicating electron-withdrawing ligands will further favor the adsorption.

Sustainable Removal of BTEX Gas Using Regenerated Metal Containing SiO2.

In the last decades, the removal of benzene, toluene, ethylbenzene, and xylene (BTEX) has been considered a major environmental crisis. In this study, two novel nanocomposite materials (Fe2O3/SiO2 and Fe2O3-Mn2O3/SiO2) that have regeneration ability by UV irradiation have been fabricated to remove BTEX at ambient temperature. This research revealed that both nanocomposites could remove more than 85% of the BTEX in the first cycle. The adsorption capacities followed the order of ethylbenzene > m-xylene > toluene > benzene as in the molecular weight order. The reusability test using UV irradiation showed that the performance of Fe2O3/SiO2 decreased drastically after the fifth cycle for benzene. On the other hand, when Mn is located in the nanocomposite structure, Fe2O3-Mn2O3/SiO2 could maintain its adsorption performance with more than 80% removal efficiency for all the BTEX for ten consecutive cycles. The difference in the reusability of the two nanocomposites is that the electron energy (from the valence band to the conduction band) for BTEX decomposition is changed due to the presence of manganese. This study provides a promising approach for designing an economical reusable nanomaterial, which can be used for VOC-contaminated indoor air.

Transition metal disulfide (MoTe2, MoSe2 and MoS2) were modified to improve NO2 gas sensitivity sensing

For the detection of the more hazardous nitrogen oxides (NO2), there is a need to find a readily fabricated, low-cost, high-performance two-dimensional material. This paper selected three transition metal disulphides (TMDs), MoTe2, MoSe2 and MoS2, as materials for detecting NO2 molecules by density flooding theory (DFT). The results show that the pure Mo(Te/Se/S)2 monolayer has a poor detection effect on NO2 molecules, and the modified monolayer exhibits better performance than its natural counterpart due to the significant electron hybridization between the dopant and the gas molecules after the introduction of metal atoms on the surface. It also leads to significant changes in electronic properties and work functions. The charge transfer mechanism based on Hirshfeld analysis shows that the charge transfer from the modified substrate to the NO2 molecule improves the binding characteristics. And by discussing the adsorption structure, adsorption energy, local electron density, density of states, and frontier orbit theory, we show that MoTe2 is a promising material for gas detection and removal, which will provide experimentalists with theoretical guidance for the application of Mo(Te/Se/S)2 based sensing materials. Our work is important for predicting novel monosulfide sensing materials and extending the application of TMDs as chemical gas sensors in the field of environmental monitoring.