Recycling of manganese ore desulfurization slag for preparation of low-temperature NH3-SCR catalyst with good scale-up production performance.

Considering the synergistic carbon/pollution reduction and resource utilization, this study proposes recycling of manganese desulfurization slag to prepare low-temperature NH3 -SCR catalyst based on solid-state ion-exchange. The desulfurization slag was hydrothermally treated to be support under mild conditions, with the parent manganese oxide ore serving as active component. Hydrothermal treatment with a desulfurization slag to NaOH mass ratio of 1.0, at 100 °C for 10 h were actually cost-effective conditions for DS recycling. The catalyst with 13.6 wt% of Mn and activated at 450 °C for 2 h in air (MO3/DSH-450 -2) performed the best, with a NO conversion of 86.9% at 150 °C and 10000 h-1, and up to 92.6% at 175 °C. Hydrothermal treatment of DS, SSIE and calcination activation resulting in a rich surface acidity and lattice oxygen of MO3/DSH, coupled with better chemical state distribution of active metal sites, promoting the NH3 -SCR activity. The scale-up produced MO3/DSH-G maintained 90.4% NOx conversion at 175 °C, showing good robustness, flexibility, and better sulfur/water resistance. The development of MO3/DSH catalyst may make full use of natural manganese ore, is a typical coupling strategy for carbon-pollutant synergistic emission reduction and resource fully utilize.

Effects of Porous Supports in Thin-Film Composite Membranes on CO2 Separation Performances.

Despite numerous publications on membrane materials and the fabrication of thin-film composite (TFC) membranes for CO2 separation in recent decades, the effects of porous supports on TFC membrane performance have rarely been reported, especially when humid conditions are concerned. In this work, six commonly used porous supports were investigated to study their effects on membrane morphology and the gas transport properties of TFC membranes. Two common membrane materials, Pebax and poly(vinyl alcohol) (PVA), were employed as selective layers to make sample membranes. The fabricated TFC membranes were tested under humid conditions, and the effect of water vapor on gas permeation in the supports was studied. The experiments showed that all membranes exhibited notably different performances under dry or humid conditions. For polyacrylonitrile (PAN) and poly(ether sulfones) (PESF) membranes, the water vapor easily condenses in the pores of these supports, thus sharply increasing the mass transfer resistance. The effect of water vapor is less in the case of polyvinylidene difluoride (PVDF) and polysulfone (PSF), showing better long-term stability. Porous supports significantly contribute to the overall mass transfer resistance. The presence of water vapor worsens the mass transfer in the porous support due to the pore condensation and support material swelling. The membrane fabrication condition must be optimized to avoid pore condensation and maintain good separation performance.

Novel catalysts with multivalence copper for organic pollutants removal from wastewater with excellent selectivity and stability in Fenton-like process under neutral pH conditions.

Fenton-like reaction has been widely used for organics degradation. However, most Fenton-like reaction works at low pH range (pH < 4) with uncontrollable selectivity of hydroxyl radicals from H2 O2 activation, and unsatisfied catalyst stability, which is compromised advanced oxidation performance for water/wastewater treatments. In this work, to solve the drawbacks, novel copper catalysts were fabricated via hydrogen reduction/calcination of Cu2+ -supported Al/MCM-41 with precisely controllable copper valence state. Compared with catalysts with monovalence copper (i.e., CuO, Cu, and Cu2+ ), the obtained catalysts with multivalence copper present higher selectivity, excellent stability towards •OH radical pathways, and outperformance in pCBA degradation efficiency at neutral state. In addition, the fabricated catalysts also exhibited excellent phenol removal efficiency (75.5%) and H2 O2 utilization efficiency (47.9%) within neutral environment. Moreover, the degradation efficiency of phenol approaches to 100% within only 2 h. The catalyst also shows good stability for organic pollutants removal, which shows good potential in catalytic oxidation for phenolic compounds-containing wastewater in Fenton-like reaction, especially under neutral pH conditions. PRACTITIONER POINTS: Multivalence copper presents great potentials for organic compounds removal at neutral condition. Multivalence copper shows higher selectivity toward •OH and good stability at neutral condition. Multivalence copper exhibiters outperformed phenol removal efficiency at neutral condition.

A novel CNTs functionalized CeO2/CNTs-GAC catalyst with high NO conversion and SO2 tolerance for low temperature selective catalytic reduction of NO by NH3.

Low-temperature selective catalytic reduction of NOx by NH3 (NH3-SCR) for diminishing SO2 poisoning remains an issue in flue gas denitrification (DeNOx). Herein, A novel CNTs functionalized low temperature NH3-SCR catalyst CeO2/CNTs-GAC was prepared, which showed high NO conversion activity (100% at 150 °C) and SO2 resistance. The addition of CNTs restrained SO2 adsorption but improved the selective adsorption of NO, which restricted the deposition of (NH4)2SO4 and/or Ce2(SO4)3, and resulted in high SO2 resistance. The addition of CNTs facilitated the diffusion and transportation of NH3 and NO, and the electron transfer on CeO2/CNTs-GAC, leading to higher content of Ce3+ and adsorbed O species on the CeO2/CNTs-GAC surface and promoted formation of surface-adsorbed oxygen OA. Therefore, CeO2/CNTs-GAC provided abundant NO adsorption and activation sites, facilitating "fast SCR" reaction and enhancing the NH3-SCR reaction. The proposed CeO2/CNTs-GAC catalyst exhibited higher NH3-SCR activity, N2 selectivity, catalytic durability and SO2 resistance than CeO2/GAC.

Hierarchical porous biochar from plant-based biomass through selectively removing lignin carbon from biochar for enhanced removal of toluene.

This study proposed a simple and green air oxidation (AO) method to prepare hierarchical porous biochar by selectively removing lignin carbon from biochar after the pyrolysis of plant-based biomass, based on the fact that the thermal decomposition temperature in air between lignin carbon and cellulose/hemicellulose carbon was different. Three kinds of biomass with different lignocellulose contents were used, including walnut shell, cypress sawdust and rice straw. The results found that AO treatment could effectively improve the pore structure of the three biochar. The specific surface area of WCO-4, CCO-4 and RCO-4 was 555.0 m2/g, 418.7 m2/g and 291.9 m2/g, respectively, which was significantly higher than those of WC (319.5 m2/g), CC (381.7 m2/g) and RC (69.6 m2/g), respectively. Among these, walnut shell biochar with air oxidation (WCO) had higher surface area of 555.0 m2/g and mesopore volume of 0.116 cm3/g, this was related to its high content of lignin, which could facilitate the formation of mesopores by AO treatment with high selectivity. The toluene adsorption capacity of WCO reached 132.9 mg/g, which increased by 223.4% from that without AO treatment. The kinetics study indicated that the diffusion rates of toluene molecule were improved due to the increased mesopores volume of biochar and micropores also play an important role in the adsorption of toluene. The results demonstrate that AO treatment is a promising method to develop hierarchical porous structure for lignocellulose-rich plant-based biomass with low cost and environmental-friendly, which greatly enhanced the toluene adsorption capacity.

From typical silicon-rich biomass to porous carbon-zeolite composite: A sustainable approach for efficient adsorption of CO2.

Focusing on the high-valued utilization of the widespread silicon-rich waste biomass, a sustainable route by simultaneous utilization of carbon and silicon from silicon-rich rice husk was proposed in this work. Specifically, porous carbon-zeolite composite with hierarchical porous structure of micro/meso pores (carbon) and ultra-microporous pores (Na-X zeolite) was in situ prepared by a facile one-pot method. The obtained porous carbon-zeolite composite (PC2-Z) had a higher yield of 67.66% compared to the porous carbon without silicon (PC2) of 43.33%. Moreover, due to the high ultra-micropore volume of the PC2-Z sample (up to 0.181 cm3/g), it exhibited high dynamic CO2 adsorption capacity of 1.81 mmol/g and CO2/N2 selectivity of 9.80 (1 bar), which were higher than 1.67 mmol/g and 7.01 (1 bar) for PC2, respectively. PC2-Z also showed good regeneration efficiency above 99% after ten cycles. Furthermore, the economic and energy consumption assessment of this utilization route was conducted. Overall, a facile one-pot route was developed to prepare highly efficient composite absorbents from silicon-rich biomass, which can be widely used in different environmental applications.

Air oxidation coupling NH3 treatment of biomass derived hierarchical porous biochar for enhanced toluene removal.

In this study, hierarchical porous biochar was prepared from poplar sawdust by air oxidation coupling with NH3 treatment for the removal of toluene. The results showed that the mesopore volume of the sample with air oxidation (PS‒O2) increased significantly to 0.263 cm3/g from the blank sample (PS, 0.053 cm3/g). This could be attributed to the selective removal of the lignin carbon by air oxidation to develop mesopores in biochar. Following further NH3 treatment (PS‒O2‒NH3), the basic surface chemistry on biochar was improved due to increased basic N-containing groups and decreased acidic O-containing groups, together with the micropore volume also increased to 0.231 cm3/g from 0.186 cm3/g of PS‒O2. The formation mechanism of hierarchical porous structure of biochar was also discussed. The adsorption capacity of PS‒O2‒NH3 for toluene reached 218.4 mg/g at the initial concentration of 820 mg/m3, which was 383.2% higher than that of PS. The adsorption isotherm study indicated that the adsorption process of toluene was monolayered and the maximal adsorption capacity of PS‒O2‒NH3 for toluene could reach as high as 476.2 mg/g. The results demonstrated that air oxidation coupling NH3 treatment is a highly effective method for the preparation of hierarchical porous biochar for enhancing toluene adsorption performance.

Continuous Synthesis of Nanodroplet-Templated, N-Doped Microporous Carbon Spheres in Microfluidic System for CO2 Capture.

Microporous carbon has been widely known as a probable material to capture greenhouse gases. This work provides a facile synthesis of monodisperse biomass-derived microporous carbon spheres (CSs) for effective CO2 capture. The spheres were synthesized by a novel continuous microfluidic strategy from oil-in-water-in-oil ((O1/W2)/O2) emulsions. O1 nanodroplets could be self-assembled into the cores of micelles, which were formed by chitosan and surfactant F127 in the W2 phase through high-speed liquid-phase shearing. The obtained O1/W2 emulsion can be further sheared into a sphere by the O2 phase. After carbonization, nanodroplet-templated pores shrank to micropores and ultramicropores. The optimal sample showed the developed pore structure with a Brunauer-Emmett-Teller (BET) surface area of 576 m2/g and microporous volume of 0.22 cm3/g. Compared with O1 free CS, the dynamic adsorption capacity of CO2 was improved to 1.20 mmol/g from 0.42 mmol/g. The CO2 capture capacity, cycling stability, isosteric heats, and mass diffusion coefficient of CSs were evaluated as well. The results demonstrate that microporous CSs are promising candidates for CO2 capture with low cost and a green synthesis route, which was achieved via continuous microfluidic strategy using sustainable biomass chitosan as a carbon precursor and droplets as templates.

Manipulation of Fibril Surfaces in Nanocellulose-Based Facilitated Transport Membranes for Enhanced CO2 Capture.

The transition toward sustainable processing entails the use of biobased alternatives as functional materials to reduce the overall carbon footprint. Nanocellulose, due to its natural availability, biodegradability, excellent mechanical properties, tunable surface, and high aspect ratio, is attracting more and more interest as a nanoscale additive in polymeric membranes. In this work, an effective way to modify nanocellulose fibril surfaces for performance enhancement in CO2 separation membranes has been demonstrated. The functionalization promptly triggered intrinsic property responses in favor of nanofiber dispersion and CO2 transport. Thin composite membranes containing the modified nanofibers in water-swelling poly(vinyl alcohol) (PVA) as well as in the blend of sterically hindered polyallylamine (SHPAA) and PVA were fabricated and tested using humid gas permeation tests. Defect-free ultrathin (300 nm) hybrid selective layers containing evenly distributed nanofibers were successfully coated. The addition of nanocellulose exhibited enhanced CO2 permeance and CO2/N2 selectivity compared to those of the neat PVA membranes. CO2 permeance up to 652 GPU and a CO2/N2 selectivity of 41.3 with SHPAA/PVA blend were documented. Functionalization plays a categorical role in the dispersion of nanocellulose fibrils in the SHPAA/PVA blend, increasing the steric stabilization and interface compatibility with the polymer matrix. The tuned interface with PEG groups act as sites for water clusters retention and increased CO2 solubility, thus creating fast diffusion pathways for CO2 transport.

Fabrication and Evaluation of Bio-Based Nanocomposite TFC Hollow Fiber Membranes for Enhanced CO2 Capture.

Nanocellulose is a promising and sustainable biobased nanomaterial because of its excellent mechanical properties, biocompatibility, natural abundance, and especially its high aspect ratio. Interest in applying nanocellulose as nanofillers in membrane fabrication has been growing rapidly in recent years. In the present work, nanocellulose crystals (CNCs) and nanocellulose fibers (CNFs) were incorporated into polyvinyl alcohol (PVA) to prepare evenly dispersed nanocomposites. The resultant nanocomposite materials containing up to 80 wt % of nanocellulose were coated as defect-free, thin-film-composite selective layers onto hollow fiber membrane substrates via dip-coating for efficient CO2 capture. Thermogravimetric analysis, Fourier-transform infrared, X-ray diffraction, scanning transmission electron microscopy, scanning electron microscopy, and humid mixed gas permeation test were used to evaluate the nanocomposite materials and the membranes. The resultant PVA/CNC nanocomposite membranes exhibit both higher CO2 permeance and CO2/N2 selectivity compared to the PVA/CNF membranes and neat PVA membranes. The addition of CNCs showed more positive effects on the CO2 permeation compared to CNFs. Under optimized conditions, CO2 permeance of 672 GPU with a CO2/N2 selectivity of 43.6 was obtained with a PVA/CNC membrane. Excellent long-term stability of the membrane was also documented within a period of up to 1 year. The interface between the polymer phase and charged CNFs is believed to form fast gas transport channels at the humid state and thus enhances CO2 permeation.

Poly(1-trimethylsilyl-1-propyne)-Based Hybrid Membranes: Effects of Various Nanofillers and Feed Gas Humidity on CO2 Permeation.

Poly(1-trimethylsilyl-1-propyne) (PTMSP) is a high free volume polymer with exceptionally high gas permeation rate but the serious aging problem and low selectivity have limited its application as CO2 separation membrane material. Incorporating inorganic nanoparticles in polymeric membranes has been a common approach to improve the separation performance of membranes, which has also been used in PTMSP based membrane but mostly with respect to tackling the aging issues. Aiming at increasing the CO2 selectivity, in this work, hybrid membranes containing four types of selected nanofillers (from 0 to 3D) were fabricated using PTMSP as the polymer matrix. The effects of the various types of nanofillers on the CO2 separation performance of the resultant membranes were systematically investigated in humid conditions. The thermal, chemical and morphologic properties of the hybrid membranes were characterized using TGA, FTIR and SEM. The gas permeation properties of the hybrid membranes were evaluated using mixed gas permeation test with the presence of water vapour to simulate the flue gas conditions. Experiments show that the addition of different fillers results in significantly different separation performances; The addition of ZIF-L porous 2D filler improves the CO2/N2 selectivity at the expenses of CO2 permeability, while the addition of TiO2, ZIF-7 and ZIF-8 increases the CO2 permeability but the CO2/N2 selectivity decreases.

Performance of Mixed Matrix Membranes Containing Porous Two-Dimensional (2D) and Three-Dimensional (3D) Fillers for CO2 Separation: A Review.

Application of conventional polymeric membranes in CO2 separation processes are limited by the existing trade-off between permeability and selectivity represented by the renowned upper bound. Addition of porous nanofillers in polymeric membranes is a promising approach to transcend the upper bound, owing to their superior separation capabilities. Porous nanofillers entice increased attention over nonporous counterparts due to their inherent CO2 uptake capacities and secondary transport pathways when added to polymer matrices. Infinite possibilities of tuning the porous architecture of these nanofillers also facilitate simultaneous enhancement of permeability, selectivity and stability features of the membrane conveniently heading in the direction towards industrial realization. This review focuses on presenting a complete synopsis of inherent capacities of several porous nanofillers, like metal organic frameworks (MOFs), Zeolites, and porous organic frameworks (POFs) and the effects on their addition to polymeric membranes. Gas permeation performances of select hybrids with these three-dimensional (3D) fillers and porous nanosheets have been summarized and discussed with respect to each type. Consequently, the benefits and shortcomings of each class of materials have been outlined and future research directions concerning the hybrids with 3D fillers have been suggested.

Performance of Nanocomposite Membranes Containing 0D to 2D Nanofillers for CO2 Separation: A Review.

Membrane technology has the potential to be an eco-friendly and energy-saving solution for the separation of CO2 from different gaseous streams due to the lower cost and the superior manufacturing features. However, the performances of membranes made of conventional polymers are limited by the trade-off between the permeability and selectivity. Improving the membrane performance through the addition of nanofillers within the polymer matrix offers a promising strategy to achieve superior separation performance. This review aims at providing a complete overview of the recent advances in nanocomposite membranes for enhanced CO2 separation. Nanofillers of various dimensions and properties are categorized and effects of nature and morphology of the 0D to 2D nanofillers in the corresponding nanocomposite membranes of different polymeric matrixes are discussed with regard to the CO2 permeation properties. Moreover, a comprehensive summary of the performance data of various nanocomposite membranes is presented. Finally, the advantages and challenges of various nanocomposite membranes are discussed and the future research and development opportunities are proposed.