Functionalized hollow siliceous spheres for VOCs removal with high efficiency and stability

Hierarchical porous carbon nanofibrous membranes with elaborated chemical surfaces for efficient adsorptive removal of volatile organic compounds from air

Volatile organic compounds (VOCs) in the air pose great health risks to humans and the environment. Adsorptive separation technology has proven effective in mitigating VOC pollution, with the adsorbent being the critical component. Therefore, the development of highly efficient adsorbent materials is crucial. Carbon nanofibers, known for their physical-chemical stability and rapid adsorption kinetics, are promising candidates for removing VOCs from the air. However, the relatively simple porous structures and inert surface chemical properties of traditional carbon nanofibers present challenges in further enhancing their application performance further. Herein, a hierarchical porous carbon nanofibrous membrane was prepared using electrospinning technology and a one-step carbonization & activation method. Phenolic resin and polyacrylonitrile were used as co-precursors, with silica nanoparticles serving as the dopant. The resulting membrane exhibited a specific surface area of up to 1560.83 m2/g and surfaces rich in functional O-/N- groups. With a synergistic effect of developed micro- and meso-pores and active chemical surfaces, the carbon nanofibrous membrane demonstrated excellent adsorption separation performance for various VOCs, with comparable adsorption capacities and fast kinetics. Moreover, the membrane displayed remarkable reusability and dynamic adsorption performance for different VOCs, indicating its potential for practical applications.

Ultrasmall Inorganic Mesoporous Nanoparticles: Preparation, Functionalization, and Application

Ultrasmall mesoporous nanoparticles (<50 nm), a unique porous nanomaterial, have been widely studied in many fields in the last decade owing to the abundant advantages, involving rich mesopores, low density, high surface area, numerous reaction sites, large cavity space, ultrasmall size, etc. This paper presents a review of recent advances in the preparation, functionalization, and applications of ultrasmall inorganic mesoporous nanoparticles for the first time. The soft monomicelles-directed method, in contrast to the hard-template and template-free methods, is more flexible in the synthesis of mesoporous nanoparticles. This is because the amphiphilic micelle has tunable functional blocks, controlled molecule masses, configurations and mesostructures. Focus on the soft micelle directing method, monomicelles could be classified into four types, i.e., the Pluronic-type block copolymer monomicelles, laboratory-synthesized amphiphilic block copolymers monomicelles, the single-molecule star-shaped block copolymer monomicelles, and the small-molecule anionic/cationic surfactant monomicelles. This paper also reviews the functionalization of the inner mesopores and the outer surfaces, which includes constructing the yolkshell structures (encapsulated nanoparticles), anchoring the active components packed on the shell and building an asymmetric Janus architecture. Then, several representative applications, involving catalysis, energy storage, and biomedicines are presented. Finally, the prospects and challenges of controlled synthesis and large-scale applications of ultrasmall mesoporous nanoparticles in the future are foreseen.

Zirconium-Based Metal Organic Frameworks for the Capture of Carbon Dioxide and Ethanol Vapour. A Comparative Study

This paper reports on the comparison of three zirconium-based metal organic frameworks (MOFs) for the capture of carbon dioxide and ethanol vapour at ambient conditions. In terms of efficiency, two parameters were evaluated by experimental and modeling means, namely the nature of the ligands and the size of the cavities. We demonstrated that amongst three Zr-based MOFs, MIP-202 has the highest affinity for CO2 (-50 kJ·mol-1 at low coverage against around -20 kJ·mol-1 for MOF-801 and Muc Zr MOF), which could be related to the presence of amino functions borne by its aspartic acid ligands as well as the presence of extra-framework anions. On the other side, regardless of the ligand size, these three materials were able to adsorb similar amounts of carbon dioxide at 1 atm (between 2 and 2.5 µmol·m-2 at 298 K). These experimental findings were consistent with modeling studies, despite chemisorption effects, which could not be taken into consideration by classical Monte Carlo simulations. Ethanol adsorption confirmed these results, higher enthalpies being found at low coverage for the three materials because of stronger van der Waals interactions. Two distinct sorption processes were proposed in the case of MIP-202 to explain the shape of the enthalpic profiles.

Enhanced removal for H2S by Cu-ordered mesoporous carbon foam

It is of great significance to protect workers from Sulphur compounds in efficient ways during the regular overhaul or emergency management. Efficient adsorbent with low pressure drop is highly desired in protective equipment. In this work, Cu-ordered mesoporous carbon foams (MeCF) were prepared through the sol-gel casting and wet-impregnation process. The obtained carbon foams possessed typical sponge structure with high porosity and copper particles attached on the skeleton. The characterization on morphology, structure and property illustrated that the presence of mesopores could effectively inhibit the growth of copper particle on MeCF. As the representative of Sulphur compounds, H₂S was selected to evaluate the protective performance. Porous copper carbon foams with moderate loading rate (3%) of copper species exhibited longest breakthrough time and largest adsorption capacity. Compared with the microporous foams, MeCF-3 displayed promoted protective performance with breakthrough time of 54.7 min and adsorption capacity of 27.8 mg/g. The enhancement on capabilities was attributed to small-sized copper species with high activity and better dispersion on mesoporous structure. These results reveled that MeCF with sponge frameworks, developed mesoporous structure and high dispersion of active species would be a promising candidate for the elimination of H₂S in personal protective equipment.

A critical review on VOCs adsorption by different porous materials: Species, mechanisms and modification methods

Volatile organic compounds (VOCs) have attracted world-wide attention regarding their serious hazards on ecological environment and human health. Industrial processes such as fossil fuel combustion, petrochemicals, painting, coatings, pesticides, plastics, contributed to the large proportion of anthropogenic VOCs emission. Destructive methods (catalysis oxidation and biofiltration) and recovery methods (absorption, adsorption, condensation and membrane separation) have been developed for VOCs removal. Adsorption is established as one of the most promising strategies for VOCs abatement thanks to its characteristics of cost-effectiveness, simplicity and low energy consumption. The prominent progress in VOCs adsorption by different kinds of porous materials (such as carbon-based materials, oxygen-contained materials, organic polymers and composites is carefully summarized in this work, concerning the mechanism of adsorbate-adsorbent interactions, modification methods for the mentioned porous materials, and enhancement of VOCs adsorption capacity. This overview is to provide a comprehensive understanding of VOCs adsorption mechanisms and up-to-date progress of modification technologies for different porous materials.

Fabrication of Functionalized Porous Silica Nanocapsules with a Hollow Structure for High Performance of Toluene Adsorption-Desorption

Functionalized mesoporous silicas are an emerging kind of adsorbents for the removal of volatile organic compounds (VOCs). Breaking the limitations of traditional mesoporous silica, in this study, porous silica nanocapsules (PSNs) functionalized with phenyl and n-octyl groups (named as p-PSN and n-PSN, respectively) were developed for the first time. Under dry conditions, the PSNs exhibited highest dynamic adsorption capacity and desorption efficiency among the ever-reported typical adsorbents (i.e., SBA-15, KIT-6, silicalite-1, and activated carbon). Under wet conditions, the functionalized PSNs made up the defects of pure PSNs, displaying excellent hydrophobicity. The Q _WET for n-PSN and p-PSN increased by 44 and 76%, respectively, as compared with that of pure PSNs in 50% relative humidity. The Henry constant of static adsorption demonstrated that p-PSN had a better capture ability for toluene, which was owing to the π-interaction between the phenyl groups and the toluene molecules. In addition, p-PSN showed considerable stability after six consecutive dynamic adsorption-desorption cycles in 50% relative humidity.

Preparation of hydrophobic hierarchical pore carbon-silica composite and its adsorption performance toward volatile organic compounds

Carbon-silica materials with hierarchical pores consisting of micropores and mesopores were prepared by introducing nanocarbon microspheres derived from biomass sugar into silica gel channels in a hydrothermal environment. The physicochemical properties of the materials were characterized by nitrogen physical adsorption (BET), scanning electron microscopy (SEM), and thermogravimetric (TG), and the adsorption properties of various organic waste gases were investigated. The results showed that microporous carbon materials were introduced successfully into the silica gel channels, thus showing the high adsorption capacity of activated carbon in high humidity organic waste gas, and the high stability and mechanical strength of the silica gel. The dynamic adsorption behavior confirmed that the carbon-silica material had excellent adsorption capacity for different volatile organic compounds (VOCs). Furthermore, the carbon-silica material exhibited excellent desorption characteristics: adsorbed toluene was completely desorbed at 150°C, thereby showing superior regeneration characteristics. Both features were attributed to the formation of hierarchical pores.

Functionalized nitrogen-doped carbon dot-modified yolk-shell ZnFe2O4 nanospheres with highly efficient light harvesting and superior catalytic activity

Volatile organic compounds (VOCs), as hazardous gaseous pollutants, have attracted much attention due to their potential threat to both human health and the environment. Accordingly, photocatalysis technology is seen as a promising technology to control low concentration VOCs due to its mild operation conditions, low energy consumption, and mineralization ability. However, there are some issues with photocatalysts, such as low light utility and fast photogenerated carrier recombination, which need to be addressed for practical applications. In this work, novel nitrogen-doped carbon dot (NCD)-modified ZnFe2O4 yolk-shell nanostructure photocatalysts were fabricated for the first time. The yolk-shell structure of ZnFe2O4 efficiently shortened the photogenerated carrier migration path and enhanced light scattering in its void, while the decorated NCDs accelerated the charge transfer from the bulk to the surface. A series of characterizations was conducted to investigate the crystal structure, elemental status, optical properties, and photocatalytic performance of the obtained composite photocatalysts. The NCD-modified ZnFe2O4 yolk-shell photocatalysts exhibited both a wide spectral absorbance and low carrier recombination, resulting in high photocatalytic activity and degradation ability towards gaseous o-dichlorobenzene. Density functional theory (DFT) calculations further revealed that the NCDs effectively promoted charge transfer and weakened the recombination of photo-generated electron-hole pairs. Additionally, in situ Fourier transform infrared (FTIR) spectroscopy was performed to investigate the degradation path in the photocatalytic process, and an electron paramagnetic resonance (EPR) radical trapping experiment was conducted to unveil the reactive oxygen species involved in the system. Combining the results obtained, the synergistic effect in the enhancement of photocatalysis between NCDs and yolk-shell ZnFe2O4 was schematically proposed.

Adsorption performance of hydrophobically modified silica gel for the vapors of n-hexane and water

An ordinary silica gel (SG-1) was chosen as the raw material and hydrophobically modified with trimethylchlorosilane under different microwave exposure. The orthogonal experiment was designed to screen the optimized modification method. The hydrophobic properties modified silica gel (SG-2) was analyzed by comparing the difference changes of surface chemistries. Then, the adsorption capacities of SG-1 and SG-2 to the n-hexane vapor and water vapor, respectively, were investigated and compared with the capacities of activated carbon and SG-3 (hydrophobically modified using the same composite modifier without microwave exposure). Meanwhile, there cyclable adsorptions of SG-2 to the two vapors were conducted while the desorptions of vacuum and heat was observed. The results showed that the effect of hydrophobic modification to SG-1 under microwave exposure was obvious and SG-2 also had a very good effect of adsorption for the n-hexane vapor. The modified silica gel shows great potential and effect for the recovery of volatile organic compounds with high content of water.

Micelle-template synthesis of hollow silica spheres for improving water vapor permeability of waterborne polyurethane membrane

Hollow silica spheres (HSS) with special interior spaces, high specific surface area and excellent adsorption and permeability performance were synthesized via micelle-template method using cetyl trimethyl ammonium bromide (CTAB) micelles as soft template and tetraethoxysilane (TEOS) as silica precursor. SEM, TEM, FT-IR, XRD, DLS and BET-BJH were carried out to characterize the morphology and structure of as-obtained samples. The results demonstrated that the samples were amorphous with a hollow structure and huge specific surface area. The growth of HSS was an inward-growth mechanism along template. Notably, we have provided a new and interesting fundamental principle for HSS materials by precisely controlling the ethanol-to-water volume ratio. In addition, the as-obtained HSS were mixed with waterborne polyurethane (WPU) to prepare WPU/HSS composite membrane. Various characterizations (SEM, TEM, FT-IR and TGA) revealed the morphology, polydispersity and adherence between HSS and WPU. Performance tests showed that the introduction of HSS can improve the water vapor permeability of composite membrane, promoting its water resistance and mechanical performance at the same time.

Novel adsorption and photocatalytic oxidation for removal of gaseous toluene by V-doped TiO2/PU under visible light

In this study, V was used as a dopant to defect into the TiO2 lattice, leading to formation of Ti(3+) and V(4+) in the lattice. The presence of Ti(3+) and V(4+) introduced into the TiO2 lattice increased the electron-hole pair generation capacity and electron-hole pair separation efficiency of the TiO2, leading to enhancement of the photocatalytic activity of the photocatalyst. Porous polyurethane (PU) was used to immobilize the V-doped TiO2 by creating chemical bonds. The use of porous substrate contributed to the increased adsorption ability of the enhanced photocatalyst, as well as expanded its application for the removal of toluene from aerosols. Under dark conditions, the V-TiO2/PU only exhibited adsorption ability for toluene treatment in aerosol. Under visible light conditions, the V-TiO2/PU exhibited high photocatalytic oxidation ability for the removal of toluene in aerosol. The photocatalytic oxidation ability was found to depend on the V to TiO2 ratio. The optimal V content in V/TiO2 for enhancing the photocatalytic activity of TiO2 was determined to be 6 wt%. Even under visible light irradiation, the 6% V-TiO2/PU sample could photocatalytically remove 80% of the toluene in 200-ppmV inlet gas, while 89.3% of the removed amount was mineralized into CO2 and H2O.

Facile preparation of hierarchically porous diatomite/MFI-type zeolite composites and their performance of benzene adsorption: the effects of NaOH etching pretreatment

Hierarchically porous diatomite/MFI-type zeolite (Dt/Z) composites with excellent benzene adsorption performance were prepared. The hierarchical porosity was generated from the microporous zeolite coated at the surface of diatom frustules and from the macroporous diatomite support. A facile NaOH etching method was employed for the first time to treat the frustule support, followed by hydrothermal growth of MFI-type zeolite at the surface of frustules previously seeded with nanocrystalline silicalite-1 (Sil-1). NaOH etching enlarged the pores on diatom frustules and further increased the coated zeolite contents (W(z)). The central macropore size of the diatom frustules increased from approximately 200-500 nm to 400-1000 nm after NaOH etching. The W(z) could reach 61.2%, while the macroporosity of the composites was largely preserved due to more voids for zeolite coating being formed by NaOH etching. The Dt/Z composites exhibited higher benzene adsorption capacity per unit mass of zeolite and less mass transfer resistance than Sil-1, evaluated via a method of breakthrough curves. These results demonstrate that etching of a diatomite support is a facile but crucial process for the preparation of Dt/Z composites, enabling the resulting composites to become promising candidates for uses in volatile organic compounds emission control.

Facile preparation of hierarchically porous diatomite/MFI-type zeolite composites and their performance of benzene adsorption: the effects of NaOH etching pretreatment

Hierarchically porous diatomite/MFI-type zeolite (Dt/Z) composites with excellent benzene adsorption performance were prepared. The hierarchical porosity was generated from the microporous zeolite coated at the surface of diatom frustules and from the macroporous diatomite support. A facile NaOH etching method was employed for the first time to treat the frustule support, followed by hydrothermal growth of MFI-type zeolite at the surface of frustules previously seeded with nanocrystalline silicalite-1 (Sil-1). NaOH etching enlarged the pores on diatom frustules and further increased the coated zeolite contents (W(z)). The central macropore size of the diatom frustules increased from approximately 200-500 nm to 400-1000 nm after NaOH etching. The W(z) could reach 61.2%, while the macroporosity of the composites was largely preserved due to more voids for zeolite coating being formed by NaOH etching. The Dt/Z composites exhibited higher benzene adsorption capacity per unit mass of zeolite and less mass transfer resistance than Sil-1, evaluated via a method of breakthrough curves. These results demonstrate that etching of a diatomite support is a facile but crucial process for the preparation of Dt/Z composites, enabling the resulting composites to become promising candidates for uses in volatile organic compounds emission control.

Controlled synthesis of hexagonal mesostructure silica and macroporous ordered siliceous foams for VOCs adsorption

The Temperature-controlled phase transformation from hexagonal mesostructure silica (HMS) to macroporous ordered siliceous foams (MOSF). HMS and MOSF exhibit higher VOCs removal capacity and recyclability compared to silica gel and activated carbon.