Cost-effective and eco-friendly synthesis of MIL-101(Cr) from waste hexavalent chromium and its application for carbon monoxide separation

"Turn-on" fluorescence sensing for sensitively detecting Cr(VI) via a guest exchange process in Cu NCs@MIL-101 composites

Copper nanoclusters (Cu NCs) are a new fluorescent material that is often used for determining metal ions, but most sensing systems are based on the "turn-off" model. Here, a "turn-on" model of fluorescence sensing for the detection of Cr(VI) was developed based on Cu NCs@MIL-101 composites. The Cu NCs@MIL-101 composites were synthesized from a simple mixture of Cu NCs and MIL-101(Cr), in which the Cu NCs were uniformly distributed in MIL-101(Cr). Notably, the fluorescence intensity of Cu NCs@MIL-101 was significantly weakened due to the internal filtration effect (IFE) of MIL-101. When Cr(VI) was introduced, the fluorescence of Cu NCs@MIL-101 was recovered by the guest exchange process between Cr(VI) and the Cu NCs, which overcame the IFE of Cu NCs@MIL-101. Based on this, a "turn-on" fluorescence probe was successfully constructed for the quantitative detection of Cr(VI) with two linear ranges of 0.05-1 μM and 1-20 μM, and a low detection limit of 0.05 μM. The proposed fluorescence probe possessed excellent selectivity and anti-interference ability, and was successfully applied for the detection of Cr(VI) in real water samples with satisfactory results. This study provides a new approach for the analytical application of Cu NCs.

PdRu Bimetallic Nanoparticles/Metal-Organic Framework Composite through Supercritical CO2-Assisted Immobilization

Metal-nanoparticle (NP)/metal-organic framework (MOF) composites have attracted considerable attention as heterogeneous catalysts. Compared with porous carbon, silica, and alumina, the charge-transfer interaction between the metal NPs and the MOF accelerated the catalytic activity. In this study, PdRu bimetallic NPs were successfully immobilized on MOFs such as MIL-101(Cr) by using supercritical carbon dioxide. The STEM-EDX images show a uniform 3D distribution of the PdRu bimetallic NPs on MIL-101(Cr). The resulting PdRu@MIL-101(Cr) catalyst exhibited higher CO oxidation than monometal/MOF composites such as Pd@MIL-101(Cr) and Ru@MIL-101(Cr). Furthermore, PdRu@MIL-101(Cr) exhibited higher catalytic activity than PdRu@SiO2. This is because the particle size of the PdRu bimetallic NPs in MIL-101(Cr) was within the range of 2-3 nm. The synergistic effects were based on the combination of two metals, Pd and Ru, small bimetal particle formation, and charge-transfer interactions between the bimetal NPs and the MOF. These factors enhance the catalytic activity of the bimetal/MOF composites.

A novel ionic liquid-entrapped MIL-101(Cr) framework with enhanced removal efficiency towards phosphate from aqueous solution

Developing adsorbent materials with high adsorptive dephosphorization (ADP) is significant for treating phosphate from aqueous solutions and eutrophic water. Herein, the MIL-101(Cr) framework was entrapped ionic liquid (IL) of 1-butyl-3-methylimidazoliumbromide ionic liquid ([C4mem]+[Br]-) using a ship-in-a-bottle approach to obtain novel adsorbents [C4mem]+[Br]-@MIL-101(Cr) contained varied IL contents, namely C4mem@MIL-101. The characterization results revealed that the formed [C4mem]+[Br]- molecules interacted with the MIL-101(Cr) frameworks, enhanced their stability, and offered additional adsorption sites. The batch adsorptions of phosphate showed that the optimized C4mem@MIL-101 adsorbent loaded with ~ 7% IL-based N content had the highest phosphate absorbing capacity of ~ 200 mg/g, outperforming the pristine MIL-101(Cr) and other adsorbents. The ADP efficiency was facilitated in the acidic media, where the phosphate ions of H2PO4- and HPO42- captured onto the C4mem@MIL-101 via several interactions, including electrostatic attraction, H-bonds, and chemical interactions. In the meantime, the coexisting anions diminished the phosphate adsorption because they competed with the pollutants at adsorption sites. Furthermore, phosphate treatment under the continuous fixed-bed conditions showed that 1 g of the polyvinyl alcohol (PVA)-mixed C4mem@MIL-101 pellets purified 25 l of water containing phosphate with a 1 mg/l concentration. The results suggest that the novel [C4mem]+[Br]-@MIL-101(Cr) structure had a high potential for treating phosphate in aqueous solutions.

Synergistic effects of layered Ti3C2TX MXene/MIL-101(Cr) heterostructure as a sonocatalyst for efficient degradation of sulfadiazine and acetaminophen in water

In this work, different mass loadings of MXene-coupled MIL-101(Cr) (MXe/MIL-101(Cr)) nanocomposites were generated through a hydrothermal process in order to investigate the potential of this nanocomposite as a novel sonocatalyst for the elimination of sulfadiazine (SD) and acetaminophen (AAP) in aqueous media. The sonocatalytic activity of different MXe/MIL-101(Cr) compositions and surface functionalities was investigated. In addition, the sonocatalytic activities at various pH values, temperatures, pollutant concentrations, catalyst dosages, initial H2O2 concentrations, and organic matter contents were investigated. The experiments on the sonocatalytic elimination of SD and AAP revealed that MXe/MIL-101(Cr) exhibited a catalytic efficiency of ∼ 98% in 80 min when the MXene loading was 30 wt% in the nanocomposite. Under optimized reaction conditions, the degradation efficiency of MXe/MIL-101(Cr) reached 91.5% for SD and 90.6% for AAP in 60 min; these values were 1.2 and 1.8 times greater than those of MXene and MIL-101(Cr), respectively. The high surface area of the MXe/MIL-101(Cr) nanocomposite increased from 4.68 m2/g to 294.21 m2/g, and the band gap of the tagged MIL-101(Cr) on the MXene surface was minimized. The superior sonocatalytic activity of MXe/MIL-101(Cr) was attributed to the effective contact interface, the effective separation rate of e- - h+ pairs through the type II heterostructure interface, and the favorable high free •OH radical production rates that promoted the degradation of SD and AAP. The solid heterointerface between MIL-101(Cr) and MXene was confirmed through Raman and FTIR analysis and was found to promote accessible •OH radical production under sonication, thus maximizing the catalytic activity of nanocomposites. The present results present an effective strategy for the design of a highly efficient, low-cost, reliable sonocatalyst that can eradicate pharmaceutical pollutants in our environment.

Carbon monoxide separation: past, present and future

Large amounts of carbon monoxide are produced by industrial processes such as biomass gasification and steel manufacturing. The CO present in vent streams is often burnt, this produces a large amount of CO2, e.g., oxidation of CO from metallurgic flue gasses is solely responsible for 2.7% of manmade CO2 emissions. The separation of N2 from CO due to their very similar physical properties is very challenging, meaning that numerous energy-intensive steps are required for CO separation, making the CO separation from many process streams uneconomical in spite of CO being a valuable building block in the production of major chemicals through C1 chemistry and the production of linear hydrocarbons by the Fischer-Tropsch process. The development of suitable processes for the separation of carbon monoxide has both industrial and environmental significance. Especially since CO is a main product of electrocatalytic CO2 reduction, an emerging sustainable technology to enable carbon neutrality. This technology also requires an energy-efficient separation process. Therefore, there is a great need to develop energy efficient CO separation processes adequate for these different process streams. As such the urgency of separating carbon monoxide is gaining greater recognition, with research in the field becoming more and more crucial. This review details the principles on which CO separation is based and provides an overview of currently commercialised CO separation processes and their limitations. Adsorption is identified as a technology with the potential for CO separation with high selectivity and energy efficiency. We review the research efforts, mainly seen in the last decades, in developing new materials for CO separation via ad/bsorption and membrane technology. We have geared our review to both traditional CO sources and emerging CO sources, including CO production from CO2 conversion. To that end, a variety of emerging processes as potential CO2-to-CO technologies are discussed and, specifically, the need for CO capture after electrochemical CO2 reduction is highlighted, which is still underexposed in the available literature. Altogether, we aim to highlight the knowledge gaps that could guide future research to improve CO separation performance for industrial implementation.

Ultrasonic spray pyrolysis synthesis of TiO2/Al2O3 microspheres with enhanced removal efficiency towards toxic industrial dyes

Developing low-cost and highly effective adsorbent materials to decolorate wastewater is still challenging in the industry. In this study, TiO₂-modified Al₂O₃ microspheres with different TiO₂ contents were produced by spray pyrolysis, which is rapid and easy to scale up. Results reveal that the modification of γ-Al₂O₃ with TiO₂ reduced the crystallite size of Al₂O₃ and generated more active sites in the composite sample. The as-synthesized Al₂O₃-TiO₂ microspheres were applied to remove anionic methyl orange (MO) and cationic rhodamine B (RB) dyes in an aqueous solution using batch and continuous flow column sorption processes. Results show that the Al₂O₃ microspheres modified with 15 wt% of TiO₂ exhibited the maximum adsorbing capacity of ∼41.15 mg g^-1 and ∼32.28 mg g^-1 for MO and RB, respectively, exceeding the bare γ-Al₂O₃ and TiO₂. The impact of environmental complexities on the material's reactivity for the organic pollutants was further delineated by adjusting the pH and adding coexisting ions. At pH ∼5.5, the TiO₂/Al₂O₃ microspheres showed higher sorption selectivity towards MO. In the continuous flow column removal, the TiO₂/Al₂O₃ microspheres achieved sorption capacities of ∼31 mg g^-1 and ∼19 mg g^-1 until the breakthrough point for MO and RB, respectively. The findings reveal that TiO₂-modified Al₂O₃ microspheres were rapidly prepared by spray pyrolysis, and they effectively treated organic dyes in water in batch and continuous flow removal processes.

Construction of PPSU-MoS2/PA-MIL-101(Cr) Membrane with Highly Enhanced Permeance and Stability for Organic Solvent Nanofiltration

Membranes with excellent separation performance and stability are needed for organic solvent nanofiltration in industrial separation and purification processes. Here we reported a newly PPSU-MoS₂/PA-MIL-101(Cr) composite membrane with high permeance, good selectivity and stability. The MIL-101(Cr) was introduced in the polyamide (PA) layer via the PIP/TMC interfacial polymerization process on a microporous PPSU-MoS₂ substrate. At a small doping amount of 0.005 wt% MIL-101(Cr), the PPSU-MoS₂/PA-MIL-101(Cr) composite membrane exhibited a high methanol permeance of 12.03 L m⁻² h⁻¹ bar⁻¹, twice higher than that of the pristine membrane without sacrificing selectivity. Furthermore, embedding MIL-101(Cr) notably enhanced the stability of the composite membrane, with permeance only decreasing by 8% after a long time operation of 80 h (pristine membrane decreased by 25%). This work demonstrated a composite membrane modified by MIL-101(Cr) with superior separation performance, which provides potential application of MOF materials for high-performance membranes in organic solvent nanofiltration and a theoretical foundation for future research in studying MOF’s influence on membrane properties.

Preparation of copper-loaded porous carbons through hydrothermal carbonization and ZnCl2 activation and their application to selective CO adsorption: Experimental and DFT calculation studies

CO is used as a raw material to produce valuable chemicals. Adsorption using solid materials can be employed to separate and recover CO from gas mixtures. In this study, cellulose-based, porous carbons were prepared via hydrothermal carbonization and ZnCl₂ activation. The prepared porous carbons were used for CO separation after CuCl loading by a facile solid-state dispersion method to induce π-complexation and eventually enhance the affinity toward CO. The sample with the highest CO uptake of 3.62 mmol g^-1 at 298 K and 101 kPa had a carbon:CuCl loading ratio of 1:1. This is the highest reported CO adsorption on porous carbons using CuCl as a π-complexation-inducing material. In addition, several factors, including the selectivity of CO against CO₂ and the cyclic stability using vacuum regeneration, demonstrated the potential for industrial applications. Density functional theory (DFT) calculations theoretically elucidated that the presence of small and well-dispersed CuCl clusters induce excellent CO-selective adsorption performance, which is in accordance with the experimental results.

Upcycling of Hazardous Metals and PET Waste derived Metal-Organic Frameworks: A Review in Recent Progress and Prospects

An intense increase in non-biodegradable plastics and waste metals is an immediate threat to the world and needs to be addressed urgently. There are several strategies deployed to control, eliminate,...

Identification of the preferential CO and SO2 adsorption sites within NOTT-401

DRIFT spectroscopy combined with DFT and QTAIM calculations, revealed the CO preferential adsorption sites within NOTT-401.

Self-supported beaded Au@Co3O4 nanowire arrays perform electrocatalytic CO2 reduction in water to syngas and water oxidation to O2

Beaded Au@Co₃O₄ nanowire arrays were prepared and function as a bifunctional electrocatalyst with outstanding electrochemical performance in producing syngas and the oxygen evolution reaction.