Pore Structure Of Adsorbents Research Articles

A Route to Selective Arsenate Adsorption in Phosphate Solutions via Ternary Metal Biopolymer Composites

With the increased need for improved adsorbents for efficient water treatment, sodium alginate (NaAlg) and chitosan (Chi) represent promising platform biopolymers for the preparation of biocomposite adsorbents for the effective removal of waterborne oxyanion (arsenate (Asi) and orthophosphate (Pi)) contaminants. The TMCs were characterized by spectroscopy (infrared (IR), SEM with an energy dispersive X-ray (SEM-EDX)), point-of-zero-charge (PZC) measurements, and dye adsorption by employing p-nitrophenol at variable pH. Based on dye adsorption results, the adsorbent surface area (SA) was 271 m2/g for Al-TMC, 286 m2/g for Fe-TMC, and 311 m2/g for Cu-TMC. This indicates the role of adsorbent pore structure and swelling in water. Further, the role of either aluminum (Al), copper (Cu), or iron (Fe) for the preparation of TMCs for the selective Asi removal in the presence of Pi as a competitor anion was evaluated. While Al, Fe, and Cu coordinate to the biopolymer framework at C=O sites, only Fe coordinates to –NH2 sites. While Al coordinated via Al-O and interfacial hydroxy groups, Cu showed the formation of Cu2(OH)3NO3 in contrast to Fe, which observed FeOOH formation. Adsorption of Asi was highest for Al-TMC (80 mg/g), followed by Fe-TMC (77 mg/g) and Cu-TMC (31 mg/g). Adsorption of Pi was highest for Al-TMC (93 mg/g), followed by Fe-TMC (66 mg/g) and Cu-TMC (17 mg/g). While Al-TMC showed the highest adsorption capacity overall, only Fe-TMC (followed by Cu-TMC) showed strong arsenate selectivity over orthophosphate. The selectivity toward Asi in presence of Pi was determined and the binary separation factor (αt/c) and the selectivity coefficient (βt) were calculated, where Cu-TMC (αt/c = 6.1; βt = 4.4) and Fe-TMC (αt/c = 8.3; βt = 5.0) exceeded Al-TMC (αt/c = 1.5; βt = 1.2). This work contributes to the field of oxyanion-selective adsorbents via judicious selection of the metal salt precursor during the synthetic design of the ternary biocomposite systems, as demonstrated herein.

Efficient adsorption and desorption of elemental mercury by ordered mesoporous cerium oxide nanoparticles derived from Ce-based metal–organic frameworks

Metal oxide-based adsorbents not only exhibit effective elemental mercury (Hg0) removal capacity but also offer suitability for wet desorption, which is a green treatment method to avoid secondary contamination of deactivated adsorbents. Nevertheless, the limited dispersing capacity of the carrier restricts the loading of active substances, hindering further enhancement of adsorption capacity. The pore structure of adsorbent is also a key factor for wet desorption. In this work, we synthesized a hollow cerium-based metal–organic framework (Ce-mesoMOF) as a sacrificial precursor to obtain ordered mesoporous cerium oxide (OM-CeO₂) via a mesoporous genetic pyrolysis-oxidation mechanism. OM-CeO2 inherits the excellent structural properties of mesoporous MOF with better catalytic activity, exhibiting strong adsorption capacity in various atmospheres (97.6 % in pure N2, 98.8 % in N2 + H2S). Wet desorption of Hg compounds and reduction of the active site can be synergized in Na2S2O3 solution. The octahedral structure with an ordered mesoporous shell greatly facilitates the mass transfer process, as evidenced by the strong adsorption capacity and fast kinetic parameters of OM-CeO2. Density functional theory analysis reveals that the conversion reaction of adsorbed Hg has a low energy barrier on the pyrolytic-oxidized OM-CeO2 and the inhibitory effect of reactive S for Hg0 adsorption transforms into a facilitating effect. This study leverages the structural advantages of ordered mesoporous MOFs in the field of Hg adsorption and imparts reactivity through modification for efficient adsorption–desorption.

Lignin-derived porous carbon with interconnected pores for bulky dye adsorption in fixed-bed systems

The porous structure of adsorbents is an important factor of their adsorption performance, especially in fixed-bed systems. In this study, we fabricated lignin-derived porous carbon (LPC-Mg) with interconnected pores, which exhibited low resistance for the transport of contaminants in water. The maximum adsorption capacity of LPC-Mg toward Rhodamine B (RhB) and Congo red (CR) was 403.2 and 735.3 mg·g−1 in the batch adsorption mode and 330.5 and 718.6 mg·g−1 in the column adsorption mode. Microporous, hierarchical porous, and commercial activated carbon were used as carbonaceous adsorbents for comparison. The RhB and CR adsorption capacity of LPC-Mg was 1.8–26.6 and 4.0–33.6 times those of other carbonaceous adsorbents at the breakthrough points in fixed-bed systems, respectively. This study developed an effective strategy toward the improvement in the adsorption efficiency of carbon-based adsorbents in fixed-bed systems.

Preparation of CPVC-based activated carbon spheres and insight into the adsorption-desorption performance for typical volatile organic compounds

Chlorinated polyvinyl chloride (CPVC)-based activated carbon spheres with smooth surfaces, good sphericity, interconnected hierarchical porous structure and high porosity have been synthesized by non-solvent induced phase separation method, followed by successive treatments of stabilization, carbonization at 450 °C in N2 atmosphere, and activation with CO2 as an agent at 900–1000 °C. The effect of activation temperatures on the textural properties of activated carbon spheres and their adsorption potential for volatile organic compounds (VOCs) under dynamic conditions is investigated. CO2 activation improves the hierarchy in the microporous range by stimulating the formation of supermicropores and significantly expands the specific surface area and pore volume of activated carbon spheres. The textural properties of adsorbents play a vital role in the adsorption performance of different VOCs. The adsorption capacity of VOC molecules can be greatly promoted by elevating specific surface area and pore volume. Due to the compatibility difference between the VOC molecules and the pore structure of adsorbents, the adsorption capacity follows the order of toluene > m-xylene > n-hexane. The adsorption isotherm of toluene on CPVC-AC1000 can be generally expressed by the Langmuir model. The adsorbents with larger average pore diameters possess a lower activation energy of desorption, which is beneficial for desorption. The carbon sphere activated at 1000 °C is a high-performance adsorbent with good reusability. Thus, the present study provides a synthesis process to produce the activated carbon spheres with high porosity from low-cost CPVC for its application in VOC adsorption.

Competitive adsorption effect during spontaneous external water imbibition in loaded gas-bearing coal and application of a normalized desorption rate model

The competitive adsorption effect of water and gas during the coal seam water injection process plays an important role in improving the coalbed methane (CBM) drainage rate of coal seams that do not meet the standards for gas drainage. However, competitive adsorption mainly occurs in the spontaneous imbibition process for coal seam water injection, which is not clear under the dual action of ground stress and gas pressure during spontaneous imbibition process. Here, some spontaneous imbibition experiments under isobaric water addition and isobaric desorption conditions are conducted using a spontaneous imbibition experimental system. The obtained results are as follows. (1) The accumulated replacement gas degree is negatively correlated with the gas pressure, which shows that the principle of spontaneous imbibition can be adopted to improve the gas drainage rate for coal seams whose gas drainage is not up to standard. (2) For spontaneous imbibition with loading stress does not change the adsorption pore structure, the average seepage pore diameter is negatively correlated with the wetting range, while the wetting range is positively correlated with the competitive adsorption effect. (3) The spontaneous imbibition process is a process of effectively wetting the pores of gas-bearing coal, which can effectively increase the pore water content and wetting uniformity. (4) A normalized desorption rate model of the relative replacement degree during spontaneous imbibition is established based on the dimensionless method. This study provides a technical method for improving the gas drainage rate for the drainage of substandard low-permeability coal seams.

Simultaneous removal of anionic and cationic dyes from wastewater with biosorbents from banana peels

AbstractUntreated banana peel (BP) is able to adsorb efficiently cationic dyes like methylene blue (MB) but weakly anionic dyes like orange G (OG). One way to enhance the sorption capacity for both dyes is to convert BP into activated carbon (BPAC) after thermochemical treatment. Among the various BPACs tested, the highest sorption capacity for both dyes was achieved when BP was modified with NaOH and pyrolyzed at 700°C (BPAC‐NaOH‐700). The pore structure of adsorbents was analyzed with scanning‐electron‐microscopy (SEM), nitrogen sorption isotherms, and mercury intrusion porosimetry (MIP), and the meso‐ and micro‐pore size distribution of BPAC‐NaOH‐700 was the narrowest one with the smallest mean value and the highest specific surface area. Equilibrium tests in batch mode were fitted with the extended Langmuir and Freundlich isotherms and used to estimate thermodynamic properties. The MB and OG sorption dynamics onto BPAC‐NaOH‐700 was approximated with the multi‐compartment model, and the external and internal mass‐transfer coefficients were estimated. The maximum sorption capacity of BPAC‐NaOH‐700 was found to be equal to 323 mg/g for MB and 76 mg/g for OG, both higher than the corresponding values for BP, and fully consistent with the high values of its surface area ( = 530 m2/g) and total pore volume ( = 1.81 cm3/g). The synergistic interaction for the sorption of both dyes onto BPAC‐NaOH‐700 was associated with a push‐pull mechanism, while the selective sorption of MB onto BPAC‐NaOH‐700 was attributed to the very slow rates of OG pore and surface diffusion in meso‐ and micro‐porosity, respectively. The adsorption was exothermic for BP, and endothermic for OG.

Experimental Study on Fractal Characteristics of Adsorption Pore Structure of Coal

The adsorption pore structure is the key affecting the technology of enhanced coal bed methane recovery (ECBM). In this paper, nitrogen adsorption measurement (NAM) and low-field nuclear magnetic resonance (NMR) methods are used to test the structural parameters of adsorption pores of four coal samples with different metamorphic degrees. Combining with the fractal theory, the applicability and the physical significance of fractal dimensions obtained from different models are analyzed. Finally, the main factors affecting the complexity of the pore size structure and the influence of fractal characteristics on the adsorption properties of coal are discussed. The results show that with the increase in the degree of metamorphism, the ranking order of the volume and the specific surface area of adsorption pores of four coal samples are long flame coal > anthracite > gas coal > coking coal. The fractal dimension D2 calculated by the Frenkel–Halsey–Hill (FHH) fractal model ranges from 2.5 to 2.9, representing the degree of the pore surface irregularity, and D3 calculated by the FHH fractal model ranges from 2.004 to 2.037, representing the complexity of pore size distribution. There is no clear quantitative relationship between the fractal dimension and the single structure parameters of adsorption pores. The more the pore diameter distribution is concentrated in the range of 2–5 nm, the larger the fractal dimension is, the higher the complexity of adsorption pore structure is; D2, which represents the irregularity of the surface of coal, has a good linear positive correlation with the maximum adsorption capacity of N2.

Magnetically derived fabrication of aligned porous poly(sulfonated polystyrene-co.-chitosan) monolith as a high efficient adsorbent for metal ions separation

Designing and tuning towards the porous structure of adsorbents is of great importance for promoting the adsorptive performance. Herein, a magnetic-induced copolymerization method is applied to generate an aligned porous structure in the aligned porous poly(SPS-co.-CTS) monolith. Typically, the aligned macropores primarily derives from the equilibrium of the magnetic dipolar force to the thermodynamic Brown force by tuning the applied magnetostatic field intensity to 25 mT. Due to the aligned macroporous structure, the monolith features with low back pressure, low mass transfer resistance and high adsorptive capacity. The hydrophilicity of the monolith surface is further improved by capping chitosan activated by amino onto its porous surface via the Hinsber reaction. Detail analyses are performed by a series of physical characterizations, by which exhibit the aligned macropores centering at 5.18 μm, specific surface reaching 54 m2 g−1 and large porosity. Finally, batch adsorption experiments confirm that the adorptive behaviors to Cu2+ ions and Co2+ ions submit to the Langmuir model and Pseudo-second order adsorption kinetics. Most intriguing, the film mass transfer ([kLa]f) has been stabilized due to the aligned macropores, thus facilitating the porous diffusion ([kLa]d) and improving the chromatographic performance of the monolith. All results demonstrate that the aligned porous poly(SPS-co.-CTS) monolith promises broad applications in the field of wastewater remediation.

Size‐Controllable Synthesis of ZIF‐8 and Derived Nitrogen‐Rich Porous Carbon for CO2 and VOCs Adsorption

AbstractIt's acknowledged that surface chemical and pore structure of adsorbent are main parameters to determine adsorption results. Herein, we prepared zeolitic imidazolate frameworks‐8 (ZIF‐8) with different average sizes (50, 120, and 2200 nm) and demonstrated their specific surface area and pore volume decreased with increasing particle size. ZIF‐8 (ZN) exhibits a large specific surface area (1626.4 m2 g−1) and total pore volume (1.088 mL g−1), but it has been shown to lack the non‐specific adsorption capacity for the adsorbate. Carbonization at 800 °C is proved to be an effective method to expose massive surface nitrogen‐containing functional groups and adjust the aperture to an appropriate pore size range for derived porous carbon of ZIF‐8 (ZCN). High nitrogen content (18.7 at. %) greatly improves the affinity for CO2 and Volatile Organic Compounds (VOCs), as explained by the density functional theory (DFT) calculation results. Meanwhile, particle size influences the pore‐forming results after carbonization directly. Among them, ZC50 generates a certain amount of narrow micropore in range of 0.7–1.0 nm, located in the optimal pore size range of CO2 adsorption calculated by Grand canonical Monte Carlo (GCMC) simulation, thus possessing the largest CO2 adsorption capacity (4.03 mmol g−1 at 25 °C). Besides, ZC120 exhibits more superior mesopore structure that could strengthen multilayer adsorption for VOCs.

Study on adsorption of low-concentration methyl mercaptan by starch-based activated carbon.

The development of a low-concentration methyl mercaptan adsorbing material for an efficient decontamination has become a hot research topic. In this study, carbonization activation was employed with starch and urea as carbon and nitrogen sources, respectively, to prepare a type of starch-based activated carbon. Subsequently, the product was used to adsorb low-concentration methyl mercaptan. Based on sorption experiments and molecular simulations, the underlying mechanism of the adsorption effect of the adsorbent's pore structure and surface oxygen- and nitrogen-containing functional groups on methyl mercaptan molecules were discussed. The results indicated that when the methyl mercaptan equilibrium concentration was 0.197mg/L, the adsorption capacity of SUAC-16-2 for methyl mercaptan was 78.16mg/g. Its adsorption performance was better than that of its previously reported counterparts. The well-developed microporous structure of SUAC-16-2 promoted the adsorption of methyl mercaptan. In addition, methyl mercaptan molecules could be broken down to produce CH3S- and H+ by the effect of the surface functional groups. Adjacent carbon atoms containing nitrogen and oxygen functional groups could better adsorb CH3S- and H+, and further strengthen the methyl mercaptan adsorption performance of activated carbon. The study could help to develop new technology for treatment of low concentration of methyl mercaptan in the air.

A well-defined hierarchically porous metal-organic framework and its application in separation and purification of steviol glycosides.

The separation and removal of stevioside from natural product steviol glycosides to obtain high-purity rebaudioside A is of great significance for the application of steviol glycosides in food, medicine, and other fields. Here, in order to explore the adsorbent pore structure suitable for the separation of stevioside and rebaudioside A, a hierarchically porous amino-functionalized metal-organic framework (HP-NH2 -MIL-53) with an appropriate and narrow pore size distribution was prepared using a modulator-induced defect-formation strategy. The results showed that the hierarchically porous structure with micropores and mesopores increased the specific surface area and exposed amino groups compared with original metal organic framework (NH2 -MIL-53), and the maximum adsorption capacity of HP-NH2 -MIL-53 for stevioside and rebaudioside A was 233.89mg/g. The narrow pore size distribution close to 3.80nm promoted the screening effect, resulting in a maximum adsorption selectivity of 4.13. This work proves that when the pore size of the adsorbent is between 1.41 and 3.80nm, it has a certain pore size screening effect on stevioside and rebaudioside A, and the hierarchically porous metal-organic frameworks provide a pre-design idea of adsorbent structure for the separation of natural products with molecular weight of 800-1000Da.

Preparation and evaluation of fine-tuned micropore biochar by lignin impregnation for CO2 and VOCs adsorption

The pore structure of adsorbent plays a critical role during the CO2 and volatile organic compounds (VOCs) adsorption. To improve the adsorption performance, fine-tuned micropore biochar was prepared by impregnation using sodium lignosulfonate as precursor. And the impregnated biochar was characterized and used as adsorbent to adsorb CO2 and VOCs (benzene and acetone). The results showed that the specific surface area (SSA) and micropore volume (Vmicropore) of impregnated biochar increased 3.27 and 5.02 times, which enhanced the CO2 adsorption amount obviously (77.02–102.88 mg/g). The pore structure of biochar was critical to CO2 capture, and high SSA, large Vmicropore and narrow aperture were benefits for the adsorption. Both Avrami fractional model and Freundlich model fitted the adsorption better, indicating the CO2 adsorption on impregnated biochar was multilayer adsorption and determined by both physical and chemical mechanisms. The adsorption was overwhelming exothermic process, thus increasing the temperature from 0 ℃ to 65 ℃ would decrease the adsorption amount by 74.22%-79.40%. High reusability (93.98%-98.21%) after 10 times adsorption-desorption cycles acknowledged the biochar was promising CO2 adsorbents. In addition, the impregnated biochar exhibited excellent VOCs adsorption performance, with the adsorption amount being 31.35–61.14 mg/g and 44.67–80.99 mg/g for benzene and acetone, respectively. All the results showed lignin impregnated biochar is a promising adsorbent for CO2 capture and pollution adsorption.

Facile fabrication of mesoporosity silica as support for solid amine CO2 adsorbents with enhanced adsorption capacity and kinetics

Solid amine adsorbents show the excellent capture performance in flue gas CO2 separation. The pore structure of adsorbent plays a crucial role in improving adsorption performance. Herein, hierarchical mesoporous silica (HMS) support with large pore volume was prepared via one template without resorting to either additives or multi-templates. The pore structure of HMS support for polyethyleneimine (PEI) resulted in larger CO2 adsorption capacity and faster adsorption kinetics when compared to the SBA-15 support with the same amount of PEI loading. At the optimal PEI loading of 70 wt% on HMS, CO2 adsorption amount is 4.21 mmol/g at 75 °C with 15 vol% CO2. Simultaneously, HMS-PEI70% adsorbent is proved to be good stability during 20 adsorption cyclic. These results demonstrate that supports with hierarchical mesoporosity provide significant advantages for CO2 capture. Finally, considering the practical application of adsorbent, the influence of capture temperature and impurity gas on capture performance has been further investigated. CO2 adsorption capacity was enhanced with the presence of water, while the SO2 has the negative effect on the capture performance due to the competitive adsorption of sulfur dioxide. This work can provide a promising composite adsorbent to realize the efficient CO2 separation from the flue gas in the future.

Deactivation Mechanisms of Engineering Adsorbents for VOCs Adsorption and the Lifetime-Prolonging Strategy

Adsorption–desorption process has been considered as a promising way for both the removal and recovery of volatile organic compounds (VOCs) from waste gases. However, during the engineering applications of the adsorbents, they would be deactivated or deteriorated. Herein, the deactivation mechanisms of different engineering VOC adsorbents (activated carbons and silica gels) by different processes or parameters have been investigated. It is found that the deactivation of adsorbents is mainly attributed to the following reasons: accumulation of VOCs in the pores, breaking of the pore structures due to the frequent-changing of processing conditions, occupation of the pores by water or other impurities, and so forth. For the temperature swing adsorption (TSA) process, the performance of adsorbents would be deteriorated by (i) the accumulation of VOCs due to incomplete desorption or (ii) the collapse of the pore structure of adsorbents (e.g., activated carbons and microporous silica gel) due to frequent cooling and heating between adsorption and desorption, respectively, leading to the deactivation of adsorbents. This phenomenon could be weakened when the pores in the adsorbents increased (e.g., the mesoporous silica gel, SG B). For the vacuum swing adsorption (VSA) process, the pore structure of adsorbents was slightly influenced during the adsorption–desorption cycles. The decrease in the adsorption capacity of adsorbents was mainly ascribed to the accumulation of VOC chemicals in the pores. In addition, in the TSA or VSA process, when the water vapor was present, the adsorption performance of adsorbents will be significantly reduced due to the occupation of adsorption sites by the water, resulting in faster deactivation. Considering the processing cost and lifetime of adsorbents, the TSA and VSA are combined together herein. The results show that, compared with the single TSA and VSA, the combined VSA–TSA process could be applied to different VOCs and improve the desorption rate of the adsorbents greatly at lower energy consumption and longer lifetime.

Effect of coalification and maceration on pore differential development characteristics of high-volatile bituminous coal

The coal type of high-volatile bituminous coal (HBC) is an important component of coalbed methane (CBM) reservoirs in China. Moreover, the accurate characterization of pore structures of coal is crucial to the exploration and development of CBM. In this work, the pore structure of vitrain and durain in high-volatile bituminous coals was detected using a scanning electron microscope, mercury intrusion porosimetry, low-temperature N2 adsorption, and low-temperature CO2 adsorption across multiple length scales and the effect of coalification and maceral on pore differential development law of HBC was analyzed. The findings reveal that at different pore size scales and the pore characteristics of different coal lithotypes under the influence of coalification are clearly different. In the same sample, the specific surface area (SSA) and total pore volume (TPV) of supermicropores in vitrain are higher than those of durain but the SSA and TPV of micropores and transition pores in vitrain are lower. The fractal results reveal that with the increase in pore size, the complexity of pore structure of coal increases. The relationship between the vitrain and durain pore fractal dimensions in different scale sections will change. At different pore size scales, the difference in pore structure in the vitrain and durain exhibits a trend of initially increasing and then decreasing with pore size. The inertinite content is positively correlated with the adsorption pore volume and SSA of vitrain and durain, and the vitrinite content is negatively correlated. Physical compaction considerably reduces the pore volume of vitrain during the early evolution stage of HBC but has no effect on durain. The pore parameters of vitrain and durain initially increase and subsequently decrease with the increase in vitrinite reflectances. The maximum value is obtained near the first coalification jump point. The evolution trend of the pore volume of vitrain and durain is consistent at different pore size scales; however, the total variation range of durain is higher than that of vitrain. The adsorption pore structure is mainly affected by asphaltification and polycondensation, whereas physical compaction has a greater impact on the seepage pore structure.

Effects of acid-based fracturing fluids with variable hydrochloric acid contents on the microstructure of bituminous coal: An experimental study

Acid based fracturing fluid (AFF) with appropriate hydrochloric acid (HCl) content is not only conducive to the exploitation of coalbed methane (ECBM), but also can reduce the cost and the risk of environmental pollution. The optimum HCl content can be obtained by FTIR, MIP, and XRD test of the treated coal samples. The results show that the lag zone reaches the minimum value of 0.09 when the HCl content is about 3%, indicating that the connectivity of coal is the best. The effect of AFF on the adsorption pore structure is sensitive to HCl content. AFF with high HCl tends to increase the amount of adsorption pores by more than 9.7%, which enhances the gas adsorption capacity and is thus not conducive to ECBM. The functional group content initially increases with increasing HCl and then decreases. When the content of HCl is about 3%, they reache the maximum value, increasing by 26.5%, 16%, 38.5%, and 48.2%. The infrared indexes show the same trend of an initial increase and then decrease with increasing HCl content, whereas the aliphatic chain length shows a weakly positive trend. The results indicate that AFF with 3%–5% HCl is the most conducive for ECBM.

The Influence of the Textural Characteristics of the Hierarchical Porous Carbons on the Removal of Lead and Cadmium Ions from Aqueous Solution

Developing efficient adsorbent materials for water treatment is deemed as one of the key solutions towards mitigating the contaminated water problem. Herein, several Hierarchical Porous Carbons (HPCs) with large mesopore volumes (up to 3 cm3/g) and a wide range of BET surface areas (747–1037 m2/g) were synthesized, and their heavy metal removal behaviors were investigated. Specifically, simulated lead and cadmium aqueous solutions were used to investigate the HPCs adsorption performance towards lead and cadmium removal. All the HPCs demonstrated high affinities towards lead removal compared with cadmium. Additionally, a systematic investigation was carried out to understand the structure—performance relationships for the HPCs. Interestingly, varying the adsorbent pore structure leads to different adsorbent behavior for lead compared with cadmium. The textural characteristics of the HPCs have a limited effect on the removal of cadmium ions. Accordingly, to expedite cadmium removal from aqueous samples, factors other than textural characteristics (i.e., surface chemistry) might enhance the removal process. Conversely, the removal of lead ions can be significantly controlled by the HPCs pore structure. HPC1221 (with 17 nm mesopore size, 2.8 cm3/g pore volume, 907 m2/g) showed the maximum adsorption capacity value of 12.32 mg/g for Cd2+ and 89 mg/g for Pb2+ compared to other HPCs. The significant adsorption parameters were evaluated using the response surface methodology (RSM) design. We believe that the reported insights for the structure–performance relationships will be useful for better designing highly efficient adsorbent materials.

ACTIVE CARBONS, OBTAINED BY THERMOCHEMICAL ACTIVATION OF RAPE STRAW

The presence of a huge amount of waste of plant origin, including annually renewable, is a high innovative resource for obtaining a variety of useful products of large and small-tonnage chemistry. Processing straw of agricultural crops into activated carbons (AC), which are successfully used in various industries and agriculture, is one of the possible directions of using agricultural waste (AIC) to obtain new functional materials with specific properties. The paper presents studies on the physicochemical properties and structural characteristics of activated carbons based on rape straw and discusses the prospects of their application for solving the most important problems of the agricultural sector. The effect of thermochemical activation temperature (650–750 °С) on the characteristics of the porous structure of adsorbents was studied. The characteristics are calculated on the basis of isotherms of low-temperature (77 K) nitrogen adsorption-desorption. Temperature dependences of the specific surface area, total pore volume, and micropore volume were obtained. It was found that KOH promotes surface development and the formation of a porous system in the entire temperature range.

Bubbling synthesis and high-temperature CO2 adsorption performance of CaO-based adsorbents from carbide slag

Carbide slag used as low-cost adsorbents for high-temperature CO2 capture has widely researched; however, the sintering at high calcination temperature often resulted in an obvious decay of CO2 capture performance after multiple CO2 capture cycles. In this work, a new strategy of synthetic CaO-based adsorbents from carbide slag via the bubbling approach was reported to stabilize the pore structure of adsorbents, to improve the sintering resistance of adsorbents and to boost the CO2 adsorption capacity. Therefore, the influences of bubbling rate, stirring rate, reaction temperature, and carbide slag dosage on CO2 adsorption capacity of CaO-based adsorbents were systemically investigated at 750 °C for 1 h. The synthetic CaO-based adsorbent from carbide slag on the basis of following conditions: 200 sccm of CO2 bubbling, 1100 rpm/stirring, 40 °C of reaction temperature and 5 g of carbide slag dosage, presented the highest CO2 adsorption capacity of 619.8 mg/g and 542.6 mg/g in the 1st and 15th cycles, which were about 6.6% and 33.9% higher than that of original carbide slag (CS). This significant improvement in CO2 uptake capacity is due to more stable interconnected and 2–5 nm porous structure in the as-prepared CaO-based adsorbent, which outstandingly lowered down the sintering of adsorbents and stabilized the CO2 adsorption capacity during multiple CO2 capture cycles.

Fabrication of superporous cellulose beads via enhanced inner cross-linked linkages for high efficient adsorption of heavy metal ions

One of the most important problems in adsorption of heavy metal ions is its slow adsorption kinetics resulting from the narrow pore structure of adsorbents. Herein, a novel superporous spherical cellulose adsorbent was fabricated by a facile yet effective preliminary chemical cross-linking strategy for high efficient adsorption of heavy metal ions. By this strategy, the neighboring cellulose chains were cross-linked and assembled into large cellulose clusters, by which unique superpores with the pore size of 0.5–1.0 μm were formed. Meanwhile, the preliminary chemical cross-linking method prevented the growth of cellulose crystallization, leading to the formation of more amorphous regions, which contributed to high specific surface area (152 m2 g−1). Further, the proposed superporous cellulose beads were modified with glutamic acid and then applied for adsorption evaluation. It was worth mentioning that the adsorbent displayed outstanding adsorption capabilities toward heavy metal ions (98.86 mg g−1 for Cu2+ and 102.29 mg g−1 for Co2+) and fast separation (equilibrium within 30 min). In addition, the cellulose beads also showed excellent recyclability and regeneration. Together with low-cost and eco-friendly cellulose support, the superporous cellulose beads are regard as green and sustainability, and have great potential for industrial application of heavy metal ions treatment.