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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.

Here, we have fabricated a bimetallic Ag–Cu-trimesate metal–organic framework at room temperature. The MOF showed rod-like morphology with a uniform distribution of Ag and Cu-sites in the MOF. The MOF has a surface area of 27.2 m2 g−1 with a mean pore diameter of 3.8 nm. The X-ray photoelectron (XPS) analysis confirmed the presence of Ag(I), Cu(I), and Cu(II) sites in the MOF. Moreover, a minor fraction of Ag as Ag0 (27.2%) was confirmed due to the reductive effect of DMF solvent. The synthesized MOF was tested for H2S removal under ambient conditions, where a maximum adsorption capacity of 69.7 mg g−1 was achieved. A novel regeneration method based on H2O2 solution partially regenerated the MOF. The diffraction pattern predicted the exceptional stability of the MOF after the adsorption–regeneration process. The XPS analysis confirmed sulfate/bisulfate (82.6%) and sulfide (17.4%) as the H2S adsorption/oxidation species. The regeneration process involved the oxidation of Ag0 and Cu(I), which resulted in appreciable adsorption capacity in the subsequent cycles. Thus, we have reported a new and economical synthesis of bimetallic MOFs and a method for the partial regeneration of the spent MOF.

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.

Three copper-based metal–organic frameworks (MOFs) with different organic linkers were synthesized for the removal of H2S gas at room temperature. The synthesized MOFs were characterized by microscopic and spectroscopic techniques to understand their structural, functional, and optical properties. The H2S adsorption capacity of MOFs calculated by column studies followed the trend: 105.6 mg g−1 (CuBDC) > 27.1 mg g−1 (CuBTC) > 1.3 mg g−1 (CuBDC-N) in dry conditions. The adsorption capacity increased in moist conditions due to an easy dissolution and dissociation of H2S in a film of water. X-ray photoelectron spectroscopy confirmed the presence of sulfur bound to Cu-sites and sulfate ions. The spent MOFs were regenerated by the successive effect of methanol and low power UV-C radiation. The regenerated CuBTC showed an exceptionally high adsorption capacity of 95.6 mg g−1 in the second cycle, which was linked to the reactivation of Cu-sites and improved surface area and porosity. The regeneration process developed in this study is a cost-effective method to recycle chemisorbed MOFs without compromising with their structural and functional integrity.

We report a rapid synthesis for the fabrication of terephthalate and trimesate metal-organic frameworks (MOFs) of Mn, Co, and Ni by ultrasonication of organic linkers with freshly prepared metal hydroxides. The MOFs were characterized by various microscopic and spectroscopic techniques to understand their structural, functional, and optical properties. MOFs with low bandgap energy (1.88-2.73 eV) showed strong absorbance in the UV-visible range. MOFs were exposed to UV irradiation for 40 h to understand their photostability. The MOFs showed decreased surface area and porosity with CoBTC as an exception. PXRD was less convincing for exploring functional changes in the UV-irradiated MOFs. XPS predicted changes in the oxidation states of metal nodes, the degradation of the organic linkers, and decarboxylation process in many of the transition MOFs. The study predicted terephthalate-based MOFs as more photostable than corresponding trimesate-based MOFs. This study is one of the first attempts in exploring photostability of MOFs with Mn, Co, and Ni as nodes.

The performance of UV-activated Fe2O3-containing ZSM-5 (UFZ5) and silica (UFS) as adsorbents for the removal of low concentration of volatile organic sulfur compounds (VOSCs) was investigated in ambient conditions. A ∼99.9% and ∼89.2% removal of 10 ppm DMDS was observed for UFZ5 and UFS, respectively, due to a higher proportion of iron in UFZ5. The N2 adsorption isotherm confirmed an unpredictable increase in the surface area and pore volume of adsorbents after the fifth adsorption-oxidation cycle, which made adsorbents highly reusable for multiple cycles. The spectroscopic analysis predicted an increase in the hydroxyl density along with the resistance of catalytic sites against sulfur deactivation, which favored the adsorption-oxidation process. The adsorption capacity of UFZ5 remained in the range of 0.12–0.22, 0.26–0.48, 0.40–0.75 mg g−1 for methyl mercaptan (MM), dimethyl sulfide (DMS), and dimethyl disulfide (DMDS), respectively which were significantly higher than those calculated for UFS. The analysis confirmed SO2, CO, CH3OH, H2O, and elemental S as by-products. The UFZ5 was found competent and robust for the treatment of VOSCs-contaminated indoor air.

This work reported the fabrication of NaMxOy-type adsorbents from air calcination of (Na, M)-trimesate metal-organic frameworks. NaMnxOy (NMO) crystallized as disc-shaped microsheets, whereas NaCoxOy (NCO) crystallized as smooth microsheets with surface deposition of polyhedral nanoparticles. The oxides have a surface area of 1.90–2.56 m2 g−1. The synthesized adsorbents were studied for low-temperature SO2 removal in breakthrough studies. The maximum adsorption capacity of 46.8 mg g−1 was recorded for NMO at 70 °C. The adsorption capacity increased with the increasing temperature due to the chemisorptive nature of the adsorption process. The capacity increased with the increasing bed loading and decreasing flow rate due to the improved SO2 retention time. The elemental mapping confirmed the uniform distribution of sulfur species over the oxide surface. X-ray diffraction showed the absence of metal sulfate nanoparticles in the SO2-exposed samples. The X-ray photoelectron analysis confirmed the formation of surface sulfate and bisulfate. The formation of oxidized sulfur species was mediated by hydroxyl groups over NMO and lattice oxygen over NCO. Thus, the work demonstrated here is the first such report on the use of NaMxOy-type materials for SO2 mineralization.

We have reported the fabrication of NaMnxOy from air calcination of (Na,Mn)-organic frameworks. The hexagonal microsheets of NaMnxOy formed irrespective of the type of organic linker or MOF morphology. The adsorption capacity of NaMnxOy was found 40–70 times higher than the precursor MOF. The best adsorbent showed the maximum adsorption capacity of 818.7 and 116.3 mg g−1 in wet and dry condition, respectively. The experimental parameters like mass of adsorbent and flow rate played a decisive role in the adsorption capacity. X-ray diffraction and photoelectron spectroscopy analyses predicted NaMnxSy, S, and MnSO4 as the reaction products. The spent adsorbent was stripped with an ammonia solution to yield ammonium sulfate (liquid fertilizer) and regenerated adsorbent. The regenerated adsorbent retained an adsorption capacity of more than 110 mg g−1 in the fourth cycle. It is the first report of NaMnxOy formation from the MOF precursor.

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.

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.

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.