H2S Adsorption Capacity Research Articles

Differential adsorption of H2S/CH4 by bituminous coal and its competitive adsorption properties

To investigate the adsorption characteristics and competitive adsorption patterns of H2S and CH4 in coal seams, we conducted a combined experimental and molecular simulation study using Ningxia Shuangma bituminous coal as the research subject. The experiments examined the adsorption of single-component H2S and CH4 gases at different temperatures and pressures, while the molecular model of bituminous coal was used to analyze the adsorption patterns of binary gas mixtures under competing conditions. Our experimental results demonstrate that both H2S and CH4 follow Langmuir’s model, with their saturated adsorption positively correlated with pressure but negatively correlated with temperature. Moreover, under identical conditions, H2S exhibits 2.43 times higher saturated adsorption than CH4. Molecular simulations reveal that temperature has a greater impact on H2S compared to CH4; both gases undergo reversible physisorption, where isosteric heat of adsorption decreases linearly with increasing amount of adsorbate molecules; interaction energy for H2S is larger in absolute value than that for CH4, indicating its stronger affinity towards coal surfaces; regarding binary component adsorption, an increase in proportion of H2S within the gas mixture leads to higher saturation adsorptions for both the mixture itself and individual H2S molecules while decreasing saturation adsorption for CH4; Coal adsorption selectivity factor for H2S/CH4 > 1. The preferential occupation of high-energy adsorption sites is more likely to be observed for H2S. The adsorption capacity and competitive adsorption capacity of H2S were greater than that of CH4.

Study on the Effect of H2S on the Adsorption of CH4, N2, and CO2 by Anthracite.

In order to study the effect of H2S on gas adsorption in a coal seam, the adsorption characteristics of single-component CO2, CH4, N2, and H2S and multicomponent H2S mixed with CO2, CH4, and N2 by anthracite were simulated by using the Grand Canonical Ensemble Monte Carlo (GCMC) method. The results show that the adsorption capacity of CO2, CH4, N2, and H2S in anthracite decreases with increasing temperature and increases with increasing pressure. The isothermal adsorption curves of CO2, CH4, N2, and H2S and different proportions of H2S/CH4, H2S/N2, and H2S/CO2 are highly consistent with the Langmuir equation, and the R 2 is above 0.99. Under different temperature and pressure conditions, the adsorption capacity of H2S and CO2 is stronger than that of coal for N2 and CH4, and the adsorption capacity difference is about 3 mmol/g. There is competitive adsorption among H2S, CO2, CH4, and N2, and H2S has a superior adsorption property. When H2S and other gases exist at the same time, the adsorption capacities of CH4, N2, and CO2 are reduced by 48-60%, 81-91%, and 51-66%, respectively.

Adsorption Mechanism and Regeneration Performance of Calcined Zeolites for Hydrogen Sulfide and Its Application.

Hydrogen sulfide (H2S) is a very toxic, acidic, and odorous gas. In this study, a calcined zeolite was used to investigate the adsorption performance of H2S. Among particle size, calcination temperature and time calcination temperature and time had significant effects on the adsorption capacity of H2S on the zeolite. The optimal calcination conditions for the zeolite were 332 °C, 1.8 h, and 10-20 mm size, and the maximum adsorption capacity of H2S was approximately 6219 mg kg-1. Calcination could broaden the channels, remove the adsorbed gases and impurities on the surface of zeolites, and increase the average pore size and point of zero net charge. As the zeolite adsorbed to saturation, it could be regenerated at the temperatures between 200 and 350 °C for 0.5 h. Compared with the natural zeolite, the adsorption capacities of dimethyl disulfide, dimethyl sulfide, toluene, CH3SH, CS2, CO2, and H2S were significantly higher on the calcined zeolite, while the adsorption capacity of CH4 was lower on the calcined zeolite. A gas treatment system by a temperature swing adsorption-regeneration process on honeycomb rotors with calcined zeolites was proposed. These findings are helpful for developing techniques for removing gas pollutants such as volatile sulfur compounds and volatile organic compounds to purify biogas and to limited toxic concentrations in the working environment.

Implantation of guanidine chemical adsorption sites in hyper-crosslinked polymers for effective adsorption and conversion of H2S

The efficient and selective separation of H2S is of critical scientific importance in the desulphurization of natural gas. In this work, we demonstrate a novel approach for incorporating guanidine chemical adsorption sites into hyper-crosslinked polymers (HCPs) for the first time. As expected, these HCPs exhibited excellent H2S adsorption capacity of up to 7.66 mmol·g−1 and high separation selectivity values of 133 for H2S/CO2 (0.15/0.85) and 977 for H2S/CH4 (0.15/0.85) at 25 °C and 1 bar. These HCPs maintained their structural stability after adsorbing H2S and successfully catalyzed the conversion of H2S to thiols with an approximate yield of 99 % under mild conditions. The results obtained from X-ray photoelectron spectroscopy (XPS), nuclear magnetic resonance (NMR), In-situ FTIR spectrometer (FTIR), and density functional theory (DFT) calculations validated that the HCPs achieved good selective trapping and catalytic conversion of H2S through chemisorption interaction and activation. This study provides valuable insights into the development of porous materials for efficient removal and conversion of H2S, while also highlights the potential of HCPs in gas separation and conversion.

Enhanced selective adsorption of H2S from CO2 by incorporating methylated polyethyleneimine into a porous carbon matrix

In this study, a series of hybrid adsorbent materials (AC@mPEI) with superior selective separation properties of H2S and CO2 are prepared by taking advantage of the differences in reaction mechanisms between H2S and CO2, as well as tertiary amines. Using a straightforward impregnation method, the methylated polyethyleneimine (mPEI) is successfully introduced into the pores of the porous carbon to create the desired hybrid adsorbents. The strong interaction between the tertiary amine groups and H2S facilitates the selective separation of H2S and CO2 gases. Remarkably, the adsorbent (1:1)AC@mPEI exhibits a substantial H2S adsorption capacity of 5.83 mmol·g−1 at 298 K and 1.0 bar and a high separation selectivity of H2S to CO2 (133), which is approximately 16.6 times higher than that of the porous carbon supporter. Further investigations, involving adsorption thermodynamics, breakthrough experiments, and spectroscopy, confirm that the strong interaction between the hybrid materials and H2S plays a pivotal role in enhancing the separation selectivity of H2S. Additionally, the adsorbed H2S can be well desorbed through vacuum degassing, allowing for multiple cycles of the adsorbent. This strategy, which leverages differences in gas adsorption mechanisms to fabricate hybrid adsorbents, presents novel concepts for the development of functional adsorbent materials for selective separation of gases.

Adsorption behavior of CO2/H2S mixtures in calcite slit nanopores for CO2 storage: An insight from molecular perspective

It is acknowledged that injecting CO2 into oil reservoirs and saline aquifers for storage is a practical and affordable method for CO2 sequestration. Most CO2 produced from industrial exhaust contains impurity gases such as H2S that might impact CO2 sequestration due to competitive adsorption. This study makes a commendable effort to explore the adsorption behavior of CO2/H2S mixtures in calcite slit nanopores. Grand Canonical Monte Carlo (GCMC) simulation is employed to reveal the adsorption of CO2, H2S as well as their binary mixtures in calcite nanopores. Results show that the increase in pressure and temperature can promote and inhibit the adsorption capacity of CO2 and H2S in calcite nanopores, respectively. CO2 exhibits stronger adsorption on calcite surface than H2S. Electrostatic energy plays the dominating role in the adsorption behavior. Electrostatic energy accounts for 97.11% of the CO2-calcite interaction energy and 56.33% of the H2S-calcite interaction energy at 10 MPa and 323.15 K. The presence of H2S inhibits the CO2 adsorption in calcite nanopores due to competitive adsorption, and a higher mole fraction of H2S leads to less CO2 adsorption. The quantity of CO2 adsorbed is lessened by approximately 33% when the mole fraction of H2S reaches 0.25. CO2 molecules preferentially occupy the regions near the pore wall and H2S molecules tend to reside at the center of nanopore even when the molar ratio of CO2 is low, indicating that CO2 has an adsorption priority on the calcite surface over H2S. In addition, moisture can weaken the adsorption of both CO2 and H2S, while CO2 is more affected. More interestingly, we find that pure CO2 is more suitable to be sequestrated in the shallower formations, i.e., 500–1500 m, whereas CO2 with H2S impurity should be settled in the deeper reservoirs.

Hydrogen Sulfide Adsorption Mechanism and Breakthrough Curves of Highly Stable Na-, Na-H-, Ca- and K-Mordenites.

Hydrogen sulfide (H2S) is a hazardous gas found in natural gas and biogas, lethal over 100 ppm. When released into the atmosphere, it can turn into sulfur dioxide. One option to remove H2S is using porous materials such as zeolites. Among them, mordenite stands out due to its channel structure, wide availability, and low cost. In this work, we evaluated the H2S adsorption capacity of mordenite using a volumetric static method. The results show the adsorption capacity of H2S in mordenite varies with the exchanged cation. The highest was measured in Na-mordenite (~4.08 mmol H2S/g mordenite). The experimental breakthrough curves for this zeolite confirmed Langmuir-type adsorption and strong affinity between Na+ cations and H2S. Despite this interaction, the XRD diffractograms of Na-mordenite show that the material retained its crystalline structure. More information about the differences in the amount of H2S adsorbed in the zeolites caused by the change in exchanged cation was obtained by H2S adsorption followed by FTIR spectroscopy. The spectra show differences in the position of the peaks related to the different adsorption modes of H2S caused by a change in the polarizing power of the cations due to their charge and position inside the zeolite pores.

In-situ regenerable Cu/Zeolite adsorbent with excellent H2S adsorption capacity for blast furnace gas

Desulfurization of blast furnace gas (BFG) is essential for steel companies to achieve its cleaner utilization. In this study, an in-situ regeneratable H2S adsorbent with a high sulfur capacity was developed. Zeolites with specific silica-aluminum ratios were selected, and hybrid Cu/zeolites adsorbents were synthesized using an impregnation method. The optimal adsorbent (DSZ-2) exhibited a high breakthrough sulfur capacity of 39.0 mg/g at 80 °C. Moreover, this adsorbent can also be in-situ regenerated at lower temperatures (280 ℃) and the regenerated adsorbent has even a higher breakthrough sulfur capacity of 49.0 mg/g. The possible desulfurization and regeneration mechanism of the DSZ-2 absorbent are discussed. Due to its high sulfur capacity and good regenerability, this absorbent has great application prospect in the removal of H2S from BFG.

Carbonaceous materials derived from biowastes pyrolysis as efficient and green biogas desulfurization system

The desulfurization performance of carbonaceous material achieved by slow pyrolysis of different kinds of organic raw biomass has been investigated to provide a greener alternative to using activated carbons and contribute to using available resources more efficiently and sustainably. Nine different raw feedstocks and biowastes were used as biomass precursors for biochar production at different pyrolysis conditions. In particular, six of them originated from lignocellulosic biomass (olive pruning, woods pruning, olive stone, spent coffee grounds, solid digestate from cattle, solid digestate from a mix of cattle and pigs), while the other three were from aquatic biomass (crabs’ blue shells, mussels’ blue shells, and microalga Chlorella sorokiniana). The H2S adsorption performances of the different biochar samples were then evaluated compared to commercial activated carbons, the technology currently in use. Moreover, the chemical composition of biochar (before and after H2S adsorption) was investigated to understand better the physical-chemical mechanism that regulated the adsorption. The results showed significant differences in the H2S adsorption capacity of biochars according to their origin (raw biomass) and operating conditions of pyrolysis (temperature and residence time), with the best performance achieved by biochar from olive pruning and microalga Chlorella. Interestingly, a combined mechanism of physio adsorption and chemical oxidation of H2S to elemental Sulphur (S) and sulphate (SO4 2-) was found.

Facile synthesis of cuprous chloride/copper chloride hydroxide composites for reactive removal of hydrogen sulfide at room temperature

In this work, a self-assembly method is developed to synthesize a series of cuprous chloride/copper chloride hydroxide composites (CCCCHs). The hydrogen sulfide (H2S) removal performances of these materials are investigated under the conditions of 25 °C, 1 atm and the inlet H2S concentration of 250 ppm in a gaseous N2 mixture with a flow rate of 40 mL min−1. It is demonstrated that the intermediate product of Cu by Fe reduction can react with CuCl2 to form cuprous chloride (CuCl). Then, CuCl2 and H2O are self-assembled on the surface of CuCl to generate the shell layer of copper chloride hydroxides (CCHs). When the molar ratio of CuCl2 to Fe is 4, the CCCCHs show the largest H2S adsorption capacity of 259.5 mg g−1 because CuCl core is almost covered by CCHs overlayers. Based on extensive results of XRD, SEM, TEM, EDS, XPS and FTIR analyses, the sulfidation reaction mechanism of CCCCHs can be revealed. When react with H2S, the CCHs surface is decomposed to generate CuCl2·2H2O and Cu2+ is reduced to Cu+, which is accompanied by the oxidation of H2S to form elemental sulfur and sulfate. During the decomposition process of CCHs, sulfidation reaction can penetrate deeply into the adsorbent particles, and the H2S treatment capacity of adsorbent is substantially improved.

Cu2O-CNF heterojunction for exhaled H2S sensing

Developing a gas sensor for the expedient, rapid, and accurate detection of hydrogen sulfide (H2S) in human exhaled breath at room temperature would offer an opportunity for home-style self-monitoring of some chronic diseases. In this work, Cu2O-carbon nanofiber (CNF) heterojunctions were prepared by a two-dimensional (2D) electrodeposition in-situ assembly method to detect low-concentration H2S gas at room temperature. The heterojunction had a distinct interface, which was confirmed by scanning electron microscopy, transmission electron microscopy and voltammetry tests. The detection limit of the sensor was as low as 5 ppb, and the sensors could directly distinguish the exhaled breath of healthy individuals and simulated patients. We attributed the excellent performances to synergistic effects of the modulation of the heterointerface barrier and the sulfide reaction of Cu2O. Furthermore, the adsorption behaviors of H2S on the surfaces of pure Cu2O and the Cu2O-CNF heterojunction were evaluated using the density functional theory (DFT) based on first principles. The results further confirmed that the formation of the heterostructure enhances the H2S adsorption capacity and electron transfer of the sensitive material. This study is of great significance for the diagnosis and monitoring of diseases with the exhaled H2S biomarker.

Characteristics of H2S at Low Adsorption Temperature using Nitrogen-enhanced Carbon Modified with Ni Nanoparticles

The main objective of this research is to investigate the adsorption characteristics of palm shell activated carbon (PSAC) adsorbent impregnated with nickel nanoparticles (Ni nps) and urea (Ni-N-PSAC) towards hydrogen sulfide (H2S) gas removal at low adsorption temperature (30°C). The impregnation of Ni nps is expected to enhance the oxygen functional groups onto the adsorbent’s structure, whereas the impregnation of urea will contribute to tailoring the nitrogen functional groups. It is expected that the Ni-N-PSAC adsorbent will exhibit heightened efficiency in removing H2S at low adsorption temperature conditions. The H2S adsorption was tested at various operating conditions such as different feed flowrate (100 – 250 ml/min), relative humidity, %RH (0 – 80 %RH) and H2S feed concentrations (1000 – 4000 ppm). The adsorption characteristics of H2S onto Ni-N-PSAC adsorbent were analyzed using adsorption isotherms and kinetics studies. The highest H2S adsorption capacity calculated was 114.66 mg H2S/g Ni-N-PSAC, where the adsorption parameters were at 100 ml/min, 30°C, 1000 ppm H2S and 40 %RH. The removal of H2S at low temperatures using Ni-N-PSAC showed that Temkin isotherm represents the best adsorption characteristics with R2 = 0.9653. The kinetic study suggests that Pseudo second-order yields the most favourable result (R2 = 0.9967). The outcome of this work is expected to provide new knowledge on the adsorption characteristics of H2S using Ni-N-PSAC adsorbent at low adsorption temperature (30°C).

Hydrogen sulfide removal from low concentration gas streams using metal supported mesoporous silica SBA-15 adsorbent

The removal of hydrogen sulfide (H2S) from gas mixtures is paramount as it can cause environmental damage, corrosion, and catalyst poisoning even at low concentration levels (100–200 mg/L). In this work, a series of Fe-Cu oxides supported SBA-15 materials were prepared using the wet incipient impregnation method with different Fe and Cu atomic ratios to evaluate the H2S removal performance. It was found that the H2S adsorption capacity generally increases with an increase in the CuO loading, with a Cu-Fe atomic ratio of 1.0:0.3 displaying the highest breakthrough H2S adsorption capacity of 74.08 mg H2S/g-sorbent. Through the XPS results, the adsorbent existed in the form of sulfate, sulfide, and elemental sulfur after reacting with H2S. In particular, it was confirmed that Fe2O3 helps to improve the H2S removal performance by creating an alkaline environment. The material with superior performance showed high capacity at low concentration compared to several published reports.

Adsorption of Hydrogen Sulfide on Activated Carbon Materials Derived from the Solid Fibrous Digestate.

The goal of this work is to develop a sustainable value chain of carbonaceous adsorbents that can be produced from the solid fibrous digestate (SFD) of biogas plants and further applied in integrated desulfurization-upgrading (CO2/CH4 separation) processes of biogas to yield high-purity biomethane. For this purpose, physical and chemical activation of the SFD-derived BC was optimized to afford micro-mesoporous activated carbons (ACs) of high BET surface area (590-2300 m2g-1) and enhanced pore volume (0.57-1.0 cm3g-1). Gas breakthrough experiments from fixed bed columns of the obtained ACs, using real biogas mixture as feedstock, unveiled that the physical and chemical activation led to different types of ACs, which were sufficient for biogas upgrade and biogas desulfurization, respectively. Performing breakthrough experiments at three temperatures close to ambient, it was possible to define the optimum conditions for enhanced H2S/CO2 separation. It was also concluded that the H2S adsorption capacity was significantly affected by the restriction to gas diffusion. Hence, the best performance was obtained at 50 °C, and the maximum observed in the H2S adsorption capacity vs. the temperature was attributed to the counterbalance between adsorption and diffusion processes.

Enriched oxygen vacancies of copper(I) oxide particles for enhanced removal of hydrogen sulfide at room temperature

In this work, the removal of hydrogen sulfide (H2S) by copper(I) oxide (Cu2O) and copper(II) oxide (CuO) particles synthesized by thermal decomposition (TD) and liquid reduction is investigated in a fixed-bed experiment at 25 °C and 1 atm. The surface oxygen vacancies (VOs) contents of the prepared Cu2O samples are more than twice that of the synthesized CuO particles, which are closely related to H2S removal performance. The H2S adsorption capacity of Cu2O prepared is 135.6 mg g−1, approximately 27 times that of CuO. A dense CuS layer formed on the CuO surface makes it significantly less reactive with H2S than Cu2O. Due to the crystal structure and abundant VOs on the Cu2O surface, the weak Cu–O bonds are broken during the sulfurization process, causing the rupture of the surface layer. And the sulfidation reaction gradually extends to the interior through the cracked surface layer, leading to the excellent sulfurization performance of Cu2O. The larger H2S adsorption capacity of Cu2O prepared by TD than that of Cu2O prepared by liquid reduction could be attributed to the presence of more numbers of VOs and Cu atoms on the surface. Moreover, H2O can enter VOs and promote the dissociation of H2S into S2−, thereby improving H2S adsorption capacity. This work demonstrates that Cu2O is a promising sorbent for H2S removal at room temperature.

Preparasi Kolom Instalasi Pemurnian Biogas dalam Penentuan Kapasitas Serap Adsorben Arang Aktif dan Zeolit di Kecamatan Jabung

Biogas is one of the alternative renewable energy sources that are useful in our lives. Kecamatan Jabung located in Malang, has the potential to produce and develop this kind of energy resources. However, biogas contains many impurities such as H2O, CO2, and H2S that could have a negative impact. Therefore, it is necessary to purify the biogas by making an installation column. The purification process is carried out by utilizing solid adsorbents including zeolite and activated charcoal. However, because solid adsorbents have a certain capacity, an integrated indicator to determine the adsorbent capacity will be needed. The existence of this indicator will be helpful for the public to monitor whether the adsorbent needs to be regenerated or replaced. According to the trial result, we may conclude that silica gel is a promising indicator to determine H2O and H2S adsorption capacity. Meanwhile, lime water can also be used as an indicator of the adsorption capacity of CO2.

Well-dispersed Cu[sbnd]Fe doping nanoparticles with mixed valence in carbon aerogel as effective adsorbent for H2S removal at low temperature

In order to overcome the deficiencies of low adsorption capacity and poor tolerance to high space velocities of commercial adsorbents for H2S removal, core-shell structured Cu-Fe/carbon aerogels (CA) with mixed valence of Cu and Fe were synthesized. The doping of Cu decreased the average size of Fe nanoparticles and enhanced the dispersion of nanoparticles. In addition, parts of oxides were reduced to Cu0 and Fe0 by carbon shell during carbonization process, resulting in the coexistence of mixed valence CuFe doped nanoparticles in CA. The existence of Cu0 and Fe0 nanoparticles is the key contributor for excellent tolerance to high space velocities, where the H2S could be easily adsorbed and dissociated to form reactive intermediate such as HS− and S2−. The well dispersed CuFe doping oxides are the active sites for H2S capture, benefiting for the high H2S adsorption capacity. The adsorbed water can be dissociated to hydroxyl groups over iron oxide, which is more conducive to the removal of H2S. The H2S (200 ppm H2S in CH4) adsorption capacity of optimized adsorbent was 221.1 mg∙g−1 at 100% relative humidity. This study provided a new insight into the synthesis of Cu-based and Fe-based adsorbents for the removal of H2S.

Effect of Catalytic Factors of Activated Carbon and Gas Stream Properties on H2S Catalytic Conversion

Catalyst-loaded activated carbons are the widely used adsorbents to remove H2S for purification of the gas streams. Virgin carbon, single, and mixed catalyst-loaded carbon are used as adsorbents. Their performance of H2S catalytic conversion was studied by evaluating their breakthrough curves in order to investigate the effect of catalyst contents, categories, assistant catalysts, and virgin carbon properties on the H2S adsorption. The effects of gas stream properties on H2S catalytic adsorption are also investigated. The results show the H2S u amount is increased with catalyst contents, and the assistant catalysts can enhance H2S catalytic conversion. NaOH-loaded carbon has better catalytic performance than KOH-loaded carbon with the same contents. Carbons after impregnation keep a relative high-pore volume between 2 and 20 nm, which is beneficial to give full play to the catalysis. The relative humidity and oxygen can enhance the H2S adsorption capacity and play important roles in H2S adsorption. CTC has little effects on the impregnated carbon for H2S catalytic conversion. Carbon impregnated with a specific catalyst can accelerate target substance adsorption and will restrict the pore volume for organics adsorption.

Kinetic and Thermodynamic Study of the Wet Desulfurization Reaction of ZnO Sorbents at High Temperatures

Hot gas conditioning is a remarkable stage for decreasing typical and harsh contaminants of syngas produced in the biomass gasification process. Downstream contaminants containing hydrogen sulphide (H2S) can significantly deteriorate fuel stream conversion reactors and fuel cell systems. Thus, an effective gas cleaning stage is required to remove critical streams that endanger the whole pathway toward the biomass conversion process. In this work, we studied H2S capture from biofuel syngas by using a kinetic deactivation model to analyze the effect of the operating conditions on the adsorption performance. Furthermore, the particle sorbent influence on other reactions, such as methane reforming and water gas shift (WGS), were also evaluated. Breakthrough curves were plotted and fitted following a first-order linearized deactivation model to perform both the H2S adsorption capacity and thermodynamic analysis. Moreover, the influence of the operating conditions was studied through a breakthrough curve simulation. By using the Arrhenius and Eyring–Polanyi expressions, it was possible to calculate the activation energy and some thermodynamic parameters from the transition state theory. Finally, a mathematical analysis was performed to obtain the diffusion coefficient (D) and the kinetic reaction constant (k¯0) of H2S gas within ZnO particles, considering a spherical geometry.

Evaluation of the H2S and NO adsorption and release capacity of PEG-zeolites and PEG-titanosilicates composites

The exogeneous delivery of hydrogen sulfide (H2S) and nitric oxide (NO) has proven to have several therapeutic effects. However, the development of porous materials to be used as drug carries, specifically as carriers of gaseous molecules, is still in its infancy. In here, we synthesized and characterized four polyethylene glycol (PEG) composites obtained from two different kinds of zeolites (4A and Y) and two titanosilicates (ETS-4 and ETS-10). The H2S and NO adsorption capacities are important aspects of the H2S/NO carriers, and they were determined for all the PEG-composites. Additionally, release studies of the H2S/NO loaded composites in aqueous solution at physiological pH revealed a longer NO release than their parent material while for H2S this was not observed, yet the % of released H2S is higher than the parent material. Cytotoxicity studies using HeLa cell line showed that PEG composites at 450 μg/mL have no toxicity. The results indicate that all PEG composites may have potential as NO-carrier, while for H2S only the 4A@PEG may be evaluated.