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MOF-199 is one of the well-studied metal–organic frameworks (MOFs) for the capture of small gas molecules. In this study, we have investigated the thermal transformation of MOF-199 microrods to CuO nanoparticles by various microscopic and spectroscopic techniques. The growth of oxide was initiated by the formation of ∼2.5 nm particles at 200 °C, which ended up as CuO nanoparticles of ∼100–250 nm size at 550 °C. An intermediate presence of Cu2O along with CuO was recorded at 280 °C. The MOF and calcined products were tested for the room-temperature desulfurization process. MOF-199 showed the maximum adsorption capacity for H2S gas (77.1 mg g–1) among all adsorbents studied. Also, MOF-199 showed a better regeneration efficiency than the derived oxide. For a sustainable process, the exhausted adsorbents were used for the photocatalytic degradation of methylene blue. The exhausted materials showed better degradation efficiencies than the fresh materials. This study reports new sustainable approaches for MOF-199 application in air and water decontamination.

Novel NaCoxOy adsorbents were fabricated by air calcination of (Na,Co)-organic frameworks at 700 °C. The NaCoxOy crystallized as hexagonal microsheets of 100–200 nm thickness with the presence of some polyhedral nanocrystals. The surface area was in the range of 1.15–1.90 m2 g−1. X-ray photoelectron spectroscopy (XPS) analysis confirmed Co2+ and Co3+ sites in MOFs, which were preserved in NaCoxOy. The synthesized adsorbents were studied for room-temperature H2S removal in both dry and moist conditions. NaCoxOy adsorbents were found ~ 80 times better than the MOF precursors. The maximum adsorption capacity of 168.2 mg g−1 was recorded for a 500 ppm H2S concentration flowing at a rate of 0.1 L min−1. The adsorption capacity decreased in the moist condition due to the competitive nature of water molecules for the H2S-binding sites. The PXRD analysis predicted Co3S4, CoSO4, Co3O4, and Co(OH)2 in the H2S-exposed sample. The XPS analysis confirmed the formation of sulfide, sulfur, and sulfate as the products of H2S oxidation at room temperature. The work reported here is the first study on the use of NaCoxOy type materials for H2S remediation.

Rapid industrialization is deteriorating air and water quality by exposing life to a wide range of pollutants, thus calling for efficient and affordable remediation strategies. Metal–organic frameworks (MOFs) are emerging materials for environmental remediation applications due to their high surface area, ordered porous structure, and application-specific tailoring of properties. In particular, transition metal-based frameworks are advanced adsorbents and catalysts for the remediation of organic and gaseous pollutants. Physicochemical properties are mainly dependent on the choice of the metal center, the oxidation state, and organic linkers. Bimetallic-, polyoxometalate-, and metal oxide-incorporated frameworks find applications as photocatalysts for decontamination of dyes, phenolic compounds, pesticides and pharmaceutical drugs under ultraviolet (UV)/visible radiations. Large surface area coupled with high activity of transition metal frameworks allows the capture and removal of inorganic and volatile organic pollutants. Transition metal frameworks convert gaseous pollutants into value-added chemicals. Frameworks containing synthetic and natural fibers are currently studied to remove chemical warfare agents.

In this study, CeO2/Fe2O3, CeO2/Mn2O3, and CeO2/Mn2O3/Fe2O3 nanocomposites were synthesized by the calcination of molten salt solutions. The microscopic images confirmed polyhedral nanocrystals of 10–20 nm size, clustered to form nanospheres. The elemental mapping confirmed the uniform distribution of transition metal oxides in the CeO2 matrix. The X-ray diffraction analysis confirmed the phase purity of metal oxides in nanocomposites. The surface area of nanocomposites was in the range of 16–21 m2 g−1. X-ray photoelectron spectroscopy confirmed 25–28% of Ce3+ ions in the CeO2 of nanocomposites. These nanocomposites were tested for the removal of hydrogen sulfide gas at room temperature. The maximum adsorption capacity of 28.3 mg g−1 was recorded for CeO2/Mn2O3/Fe2O3 with 500 ppm of H2S gas and 0.2 L min−1 of flow rate. The adsorption mechanism probed by X-ray photoelectron spectroscopy showed the presence of sulfate as the only species formed from the oxidation of H2S, which was further confirmed by ion chromatography. Thus, the study reports room-temperature oxidation of H2S over mixed metal composites, which were synthesized by a novel one-step approach.

The catalytic oxidation of volatile organic compounds (VOCs) has been studied in a series of bimetal (Fe-Co)-incorporated ZSM-5 zeolites. The bimetal incorporation was varied. The first sample was prepared by an in situ hydrothermal synthesis method (named IHT) in which both metals were added simultaneously during gel formation. The second sample was made by preparing Fe-ZSM-5 in situ and then impregnated with Co (named FIC), while the third sample was the reverse of the second sample (Co-ZSM-5 impregnated with Fe; named CIF). The objective was to find a method that yields a catalyst with high activity towards complete removal and oxidation of VOCs and is stable. All three synthesized catalysts were thoroughly characterized by modern instrumental methods, such as X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, Fourier transform infrared analysis, inductively coupled plasma optical emission spectroscopy, N2 adsorption-desorption analysis, and BET surface area. From the results, it is clear that the IHT sample has the best characteristics for the removal of VOCs and is more stable.

Oil/water separation is an important issue in the environmental field because of increasing worldwide oil pollution. In particular, emulsion under 20 μm in size causes a serious problem in water treatment. Thus, development of an effective oil/water emulsion separation membrane is required. Asymmetric wettability is one effective technique for emulsion separation due to its directional liquid transport property. In this research, wettability was controlled by adjusting the diameter of an electrospun nanofiber for a difference in surface roughness. Through analysis of the surface structure and contact angle of nanofibers with various diameters, the contact angles of fibers with different diameters were increased about 40° to confirm that surface structure affects surface wettability. Comparison of asymmetric wettability membranes (AwENMs) and a single membrane (ENM) for oil/water emulsion separation shows that AwENMs perform about two times faster and reject 10% of emulsion.

In this study, electrospun nanofiber was continuously sandwiched between two rubber rollers at high temperature (150 °C). The prepared nanofiber support layer possessed a pore size of 0.4 μm (with narrow distribution) and a fiber diameter of 292 ± 94 nm. Afterward, an interfacial polymerization was employed to deposit the selective polyamide layer on the nanofiber support layer. For the first time, engineered osmosis (EO) was used as a platform for verifying the presence of a polyamide selective layer on a nanofiber support layer. We found that the membrane prepared exhibited an excellent combination of permeability (30 L/m2h) and selectivity (17 g/m2h and 0.57 g/L) under a net pressure of 49 bar at the EO platform. The membrane developed can be applied to generate renewable energy using the EO process. In addition, the EO method can be used to detect selective polymer having a nano-scale thickness.

We report H2S gas removal using UV-irradiated Fe2O3-containing ZSM-5 (UV-Fe@ZSM-5) and Silica (UV-Fe@Silica) via adsorption-oxidation process at room temperature. The UV-irradiated adsorbents showed an increased H2S removal performance (∼12.6–17.8%) compared to the un-irradiated adsorbents. Maximum adsorption efficiency of 83.4% was recorded for UV-Fe@ZSM-5 in the optimized conditions (10 ppm of H2S, 0.5 g L‒1 of adsorbent, 90 min). The kinetic data fitted to the intra-particle diffusion indicating H2S adsorption as a pore diffusion phenomenon. Among the two adsorbents, UV-Fe@ZSM-5 was found highly reusable where the adsorption performance of 76% reached 46% in the tenth cycle. The adsorbents showed good structural stability, which was also translated in their X-ray diffraction patterns. The X-ray photoelectron spectroscopic analysis showed absence of S in the adsorbents suggesting complete oxidation of adsorbed H2S gas. In the low concentration study (1 ppm H2S), UV-Fe@ZSM-5 outperformed UV-Fe@silica, and within 30 min the concentration dropped below 0.7 ppb.

Zn-MOF/ZnO nanocomposites with different organic linkers were fabricated by a rapid ultrasonication method using freshly prepared Zn(OH)2 precipitate. The high metal-to-ligand ratio led to the simultaneous formation of MOFs and ZnO nanoparticles in the MOFs. The surface area was in the range of 12–21 m2 g−1. The nanocomposites were tested for H2S adsorption at room temperature, where the maximum adsorption capacity of 14.2 mg g−1 was recorded for ZnBTC/ZnO in dry conditions. The spent adsorbents were regenerated using methanol and UV irradiation as individual and combined strategies. The successive effect of methanol and UV radiation led to an increased adsorption capacity in the second cycle. The spectroscopic investigation of spent ZnBDC/ZnO confirmed the chemisorption of H2S over Zn-sites via Zn2+−S2− interaction. The XPS analysis of regenerated ZnBDC/ZnO confirmed a decreased sulfur content and decreased Zn ionic character. The regeneration work in this study is one of the first attempts and could be extrapolated to well-studied Zn-MOFs like MOF-5 for the desulfurization process.

In this work, a piezoelectric electrospun nanofiber membrane (pENM) was prepared to confirm its antifouling ability through the vibrational inducement of fluid instability. For the optimization of the pENM properties, the synthetic conditions (solvent ratio, tip-to-collector distance (TCD), and heat treatment time) were adjusted. The optimized properties were observed at a 5/5 acetone/N-methyl-2-pyrrolidone (NMP) solvent ratio, a TCD of 20 cm, and a heat treatment time of 0.5 h. The optimized pENM exhibited three times higher water permeability (5573 LMH/bar) and rejection performance (99.87%) for particulates than a commercial microfiltration (MF) membrane. The flux decline was reduced by 15% in the presence of a piezoelectric effect when compared to the flux decline in the absence of a piezoelectric effect. This result shows that the pENM has potential for water-treatment applications.

A mixed ligand Cu-based MOF, Cu(BDC)0.5(BDC-NH2)0.5 was synthesized by a rapid ultrasonication method for the adsorptive removal of hydrogen sulfide (H2S) gas at room temperature. The MOF has a sheet-like morphology with 100 nm thickness crystallized in the monoclinic symmetry (a = 11.27 A, b = 14.82 A, c = 7.95 A, β = 110.8°) with C2/m space group. The surface area and pore volume was 19.4 m2 g−1 and 0.024 cm3 g−1, respectively. The XPS analysis confirmed a near equal proportion of Cu(I) and Cu(II)-sites in the MOF. The MOF showed the H2S adsorption capacity of 128.4 mg g−1 for 500 ppm of H2S flowing at a rate of 100 mL min−1, which is among the highest values reported for Cu-based MOFs. The spent MOF was regenerated by a methanol and UV-irradiation method, which significantly improved the adsorption capacity. The H2S adsorbed onto the MOF by breaking Cu-carboxylate bonds with the formation of covellite CuS nanoparticles and sulfates. The spectroscopic analysis predicted a Cu(OH)-type sites after UV-irradiation along with increased surface area, which were responsible for an enhanced adsorption capacity of the regenerated sample.

Correction for ‘Terephthalate and trimesate metal–organic frameworks of Mn, Co, and Ni: exploring photostability by spectroscopy’ by Nishesh Kumar Gupta et al., RSC Adv., 2021, 11, 8951–8962, DOI: 10.1039/D1RA00181G.

A new and facile one-step synthesis method for preparing granulated mesoporous carbon (GMC) with three-dimensional spherical mesoporous symmetry is prepared to remove large molecular weight organic compounds in aqueous phase. GMC is synthesized in a single step using as-synthesized mesoporous carbon particles and organic binders through a simple and economical synthesis approach involving a simultaneous calcination and carbonization process. Characterization results obtained from SEM, XRD, as well as surface and porosity analysis indicate that the synthesized GMC has similar physical properties to those of the powdered mesoporous carbon and maintains the Brunauer-Emmett-Teller (BET) surface area and pore volume because the new synthesis method prevents the collapse of the pores during the granulation process. Batch adsorption experiments revealed GMC showed a substantial adsorption capacity (202.8 mg/g) for the removal of methyl violet as a target large molecular contaminant in aqueous phase. The mechanisms and dynamics modeling of GMC adsorption were also fully examined, which revealed that surface diffusion was rate limiting step on adsorption process of GMC. Adsorption kinetics of GMC enables 3 times faster than that of granular activated carbon in terms of surface diffusion coefficient. This is the first study, to the best of our knowledge, to synthesize GMC as an adsorbent for water purification by using facile granulation method and to investigate the adsorption kinetics and characteristics of GMC. This study introduces a new and simple method for the synthesis of GMC and reveals its adsorption characteristics for large molecular compounds in a water treatment.

The influence of the electrospinning parameters on the diameter of the polyethersulfone (PES) nanofibers was demonstrated using response surface methodology. The electrospinning parameters studied were lithium chloride (LiCl) concentration, PES concentration, feed rate, and tip-to-collector distance. The average fiber diameter was correlated to these factors by using a second-order polynomial function at a 95% confidence level. The statistical analysis indicated that LiCl concentration, PES concentration, and feed rate had the significant connection with the fiber diameter, and LiCl concentration was the most important factor in determining the fiber diameter. When LiCl concentration increased, the fiber diameter decreased, because with more LiCl that is added, more applied voltage is needed to overcome the electrostatic attractions. The interactive effect between PES concentration and feed rate, the interactive effect between PES concentration and tip-to-collector distance, and the quadratic coefficients of LiCl concentration were also found to be significant. The adjusted determination coefficient (Radj2) of the model was calculated to be 0.9106. The water flux measurements showed that the decrease in the fiber diameter of the membrane caused the decrease in the initial pure water flux. The retention tests with 0.6 &mu, m polystyrene (PS) suspension indicated that as the fiber diameter decreased, the pore sizes decreased and the particle removal efficiency increased.

The membrane processes have received extensive attention as comprehensive and interdisciplinary approaches for water-energy nexus. Nanotechnology has induced significant attention in improving membrane performances to mitigate global water and energy scarcity because of its unique characteristics and simple application for membrane fabrication. Nano-sized materials could provide highly enhanced characteristics to a membrane material, resulting in excellent performance enhancement, such as permeability, selectivity, and fouling resistance, of membrane. Carbon Nanotube (CNT), a widely utilized or studied nanomaterial in membrane science, is discussed in this chapter with a focus on its state-of-the-art applications and future prospects. Electrospun nanofiber, which is one of the feasible nano-structured membrane materials, is also discussed as a promising material for water-energy nexus. Therefore, this chapter also describes its application cases and its potential as an innovative membrane for water-energy nexus.

Granular mesoporous silica SBA-15 (GMS) synthesized by a new and facile one step method was investigated to remove a series of pharmaceutical compounds from aqueous solutions. Characterization results obtained from TEM, XRD, and surface and porosity analyzer reveal that GMS synthesized by using inorganic and organic binder has similar pore properties with the powder-type mesoporous silica SBA-15 and does not severely reduce the Brunauer–Emmett–Teller (BET) surface area and pore volume by preventing destruction of the pores after granulation step through new synthesis method. Evaluation of GMS as an adsorbent based on adsorption kinetic, isotherm, and effect of pH shows the great adsorption capacity for selected 12 selected pharmaceuticals removal in aqueous solution. In addition, the adsorption and regeneration efficiency of GMS was maintained for given adsorption-regeneration cycles. Moreover, the column experiment to remove pharmaceuticals in industrial pharmaceutical wastewater revealed that GMS has a great potential for its real field application.

The application of electrospun nanofiber membranes (ENMs) as microfilters for the process of water purification requires the substrate to possess suitable strength, permeability, and a smooth surface. Therefore, the fiber homogeneity, inter-fiber adhesion, and surface roughness of the ENMs must be carefully controlled. Concurrently, an understanding of the ENMs' rejection mechanism for contaminants is necessary for the effective application of ENMs. In this study, we demonstrate the fabrication of polyethersulfone (PES) ENMs, which are useful for water purification as water treatment membranes. An optimum fabrication condition that can significantly improve the mechanical property and surface roughness of the PES membrane is also illustrated. This technique induces the solvent remaining on the fiber's surface after the electrospinning process, and the mechanical properties and surface roughness of the membrane are improved by the solvent-induced fusion of the fiber. The fabricated PES ENMs also show higher clean water productivity. Additionally, we show that a particulate contaminant in water is mainly rejected on the ENM surface by using a water filtration test. Based on our conclusions, we suggest the appropriate ENM regeneration method and confirm that the fabricated ENMs show excellent regeneration ability.