Bimetallic Copper-Cerium-Based Metal-Organic Frameworks for Selective Carbon Dioxide Capture.

Metal-organic frameworks (MOFs) are highly regarded as valuable adsorbent materials in materials science, particularly in the field of CO2 capture. While numerous single-metal-based MOFs have demonstrated exceptional CO2 adsorption capabilities, recent advancements have explored the potential of bimetallic MOFs for enhanced performance. In this study, a CuCe-BTC MOF was synthesized through a straightforward hydrothermal method, and its improved properties, such as high surface area, smaller pore size, and larger pore volume, were compared with those of the bare Ce-BTC. The impact of the Cu/Ce ratio (1:4, 1:2, 1:1, and 3:2) was systematically investigated to understand how adding a second metal influences the CO2 adsorption performance of the Ce-BTC MOF. Various characterization techniques, including scanning electron microscopy, transmission electron microscopy, powder X-ray diffraction, thermogravimetric analysis, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and N2 BET surface area analysis, were employed to assess the physical and chemical properties of the bare Ce-BTC and CuCe-BTC samples. Notably, CuCe-BTC-1:2 exhibited superior surface area (133 m2 g-1), small pore size (3.3 nm), and large pore volume (0.14 cm3 g-1) compared to the monometallic Ce-BTC. Furthermore, CuCe-BTC-1:2 demonstrated a superior CO2 adsorption capacity (0.74 mmol g-1), long-term stability, and good CO2/N2 selectivity. This research provides valuable insights into the design of metal-BTC frameworks and elucidates how introducing a second metal enhances the properties of the monometallic Ce-BTC-MOF, leading to improved CO2 capture performance.

Impact of Surface Defects on LaNiO3 Perovskite Electrocatalysts for the Oxygen Evolution Reaction.

Perovskite oxides are regarded as promising electrocatalysts for water splitting due to their cost-effectiveness, high efficiency and durability in the oxygen evolution reaction (OER). Despite these advantages, a fundamental understanding of how critical structural parameters of perovskite electrocatalysts influence their activity and stability is lacking. Here, we investigate the impact of structural defects on OER performance for representative LaNiO3 perovskite electrocatalysts. Hydrogen reduction of 700 °C calcined LaNiO3 induces a high density of surface oxygen vacancies, and confers significantly enhanced OER activity and stability compared to unreduced LaNiO3 ; the former exhibit a low onset overpotential of 380 mV at 10 mA cm-2 and a small Tafel slope of 70.8 mV dec-1 . Oxygen vacancy formation is accompanied by mixed Ni2+ /Ni3+ valence states, which quantum-chemical DFT calculations reveal modify the perovskite electronic structure. Further, it reveals that the formation of oxygen vacancies is thermodynamically more favourable on the surface than in the bulk; it increases the electronic conductivity of reduced LaNiO3 in accordance with the enhanced OER activity that is observed.

Mercury-bearing wastes: Sources, policies and treatment technologies for mercury recovery and safe disposal.

Due to the lenient environmental policies in developing economies, mercury-containing wastes are partly produced as a result of the employment of mercury in manufacturing and consumer products. Worldwide, the presence of mercury as an impurity in several industrial processes leads to significant amounts of contaminated waste. The Minamata Convention on Mercury dictates that mercury-containing wastes should be handled in an environmentally sound way according to the Basel Convention Technical Guidelines. Nevertheless, the management policies differ a great deal from one country to another because only a few deploy or can afford to deploy the required technology and facilities. In general, elemental mercury and mercury-bearing wastes should be stabilized and solidified before they are disposed of or permanently stored in specially engineered landfills and facilities, respectively. Prior to physicochemical treatment and depending on mercury's concentration, the contaminated waste may be thermally or chemically processed to reduce mercury's content to an acceptable level. The suitability of the treated waste for final disposal is then assessed by the application of standard leaching tests whose capacity to evaluate its long-term behavior is rather questionable. This review critically discusses the main methods employed for the recovery of mercury and the treatment of contaminated waste by analyzing representative examples from the industry. Furthermore, it gives a complete overview of all relevant issues by presenting the sources of mercury-bearing wastes, explaining the problems associated with the operation of conventional discharging facilities and providing an insight of the disposal policies adopted in selected geographical regions.

Mercury in natural gas streams: A review of materials and processes for abatement and remediation.

The role of natural gas in mitigating greenhouse gas emissions and advancing renewable energy resource integration is undoubtedly critical. With the progress of hydrocarbons exploration and production, the target zones become deeper and the possibility of mercury contamination increases. This impacts on the industry from health and safety risks, due to corrosion and contamination of equipment, to catalyst poisoning and toxicity through emissions to the environment. Especially mercury embrittlement, being a significant problem in LNG plants using aluminum cryogenic heat exchangers, has led to catastrophic plant incidents worldwide. The aim of this review is to critically discuss the conventional and alternative materials as well as the processes employed for mercury removal during gas processing. Moreover, comments on studies examining the geological occurrence of mercury species are included, the latest developments regarding the detection, sampling and measurement are presented and updated information with respect to mercury speciation and solubility is displayed. Clean up and passivation techniques as well as disposal methods for mercury-containing waste are also explained. Most importantly, the environmental as well as the health and safety implications are addressed, and areas that require further research are pinpointed.

Interfacial separation of concentrated dye mixtures from solution with environmentally compatible nitrogenous-silane nanoparticles modified with Helianthus annuus husk extract.

The capacity of an adsorbent to bind and remove dye from solution greatly depends on the type of functionalization present on the nanoparticles surface, and its interaction with the dye molecules. Within this study, nitrogenous silane nanoparticles were hydrothermally synthesized resulting in the formation of rapid and highly efficient adsorbents for concentrated mixed dyes. The amorphous silane nanoparticles exhibited a monolayer based mechanism of mixed dye adsorption with removal capacities between 416.67 and 714.29 mg/g of adsorbent. Dye removal was predominantly due to the electrostatic attraction between the positively charged silane nanoparticles (13.22-8.20 mV) and the negatively charged dye molecules (-54.23 mV). Addition of H. annuus extract during synthesis resulted in three times the surface area and 10 times increased pore volume compared to the positive control. XPS analysis showed that silane treatments had various nitrogen containing functionalities at their surface responsible for binding dye. The weak colloidal stability of silane particles (13.22-8.20 mV) was disrupted following dye binding, resulting in their rapid coagulation and flocculation which facilitated the separation of bound dye molecules from solution. The suitability for environmental applications using these treatments was supported by a bacterial viability assay showing >90% cell viability in treated dye supernatants.

Fabrication of a novel ZnIn2S4/g-C3N4/graphene ternary nanocomposite with enhanced charge separation for efficient photocatalytic H2 evolution under solar light illumination.

Design and synthesis of efficient photocatalyst systems for a large volume of hydrogen (H2) evolution under solar light is still a great challenge. To obtain high photocatalytic activity, graphene-based semiconductor photocatalysts are gaining heightened attention in the field of green and sustainable fuel production due to their good electronic properties, high surface area and chemical stability. Herein, we demonstrate an efficient, novel and smart architecture of a graphene-based ZnIn2S4/g-C3N4 nanojunction by a simple hydrothermal process for H2 generation. In the present study, graphene (G) is chosen as the electron mediator and ZnIn2S4 (ZIS) and g-C3N4 (CN) are chosen as two different semiconductor photocatalysts to construct a smart architecture for the ternary photocatalytic system. Different characterization techniques such as XRD, TGA, FT-IR, SEM, TEM, HR-TEM, XPS, BET, and UV-vis DRS were employed to ensure the successful integration of graphene, ZnIn2S4, and g-C3N4 in the nanocomposite. As a result, high and efficient H2 evolution (477 µmol h-1 g-1) is attained for the graphene-based ZnIn2S4/g-C3N4 nanocomposite. Transient photocurrent experiments, ESR, PL, and time-resolved PL studies suggested that the intimate ternary nanojunction effectively promotes fast charge transfer and thereby enhances photocatalytic H2 evolution.

CeO2-Decorated ?-MnO2 Nanotubes: A Highly Efficient and Regenerable Sorbent for Elemental Mercury Removal from Natural Gas.

CeO2 nanoparticle-decorated ?-MnO2 nanotubes (NTs) were prepared and tested for elemental mercury (Hg0) vapor removal in simulated natural gas mixtures at ambient conditions. The composition which had the largest surface area and a relative Ce/Mn atomic weight ratio of around 35% exhibited a maximum Hg0 uptake capacity exceeding 20 mg?g?1 (2 wt %), as determined from measurements of mercury breakthrough which corresponded to 99.5% Hg0 removal efficiency over 96 h of exposure. This represents a significant improvement in the activity of pure metal oxides. Most importantly, the composite nanosorbent was repeatedly regenerated at 350 ?C and retained the 0.5% Hg0 breakthrough threshold. It was projected to be able to sustain 20 regeneration cycles, with the presence of acid gases, CO2, and H2S, not affecting its performance. This result is particularly important, considering that pure CeO2 manifests rather poor activity for Hg0 removal at ambient conditions, and hence, a synergistic effect in the composite nanomaterial was observed. This possibly results from the addition of facile oxygen vacancy formation at ?-MnO2 NTs and the increased amount of surface-adsorbed oxygen species.

Role of Ceria in the Design of Composite Materials for Elemental Mercury Removal.

The necessity to drastically act against mercury pollution has been emphatically addressed by the United Nations. Coal-fired power plants contribute a great deal to the anthropogenic emissions; therefore, numerous sorbents/catalysts have been developed to remove elemental mercury (Hg0 ) from flue gases. Among them, ceria (CeO2 ) has attracted significant interest, due to its reversible Ce3+ /Ce4+ redox pair, surface-bound defects and acid-base properties. The removal efficiency of Hg0 vapor depends among others, on the flue gas composition and temperature. CeO2 can be incorporated into known materials in such a way that the abatement process can be effective at different operating conditions. Hence, the scope of this account is to discuss the role of CeO2 as a promoter, active phase and support in the design of composite Hg0 sorbents/catalysts. The elucidation of each of these roles would allow the integration of CeO2 advantageous characteristics to such degree, that tailor-made environmental solution to complex issues can be provided within a broader application scope. Besides, it would offer invaluable input to theoretical calculations that could enable the materials screening and engineering at a low cost and with high accuracy.

Skin color-specific and spectrally-selective naked-eye dosimetry of UVA, B and C radiations.

Spectrally-selective monitoring of ultraviolet radiations (UVR) is of paramount importance across diverse fields, including effective monitoring of excessive solar exposure. Current UV sensors cannot differentiate between UVA, B, and C, each of which has a remarkably different impact on human health. Here we show spectrally selective colorimetric monitoring of UVR by developing a photoelectrochromic ink that consists of a multi-redox polyoxometalate and an e- donor. We combine this ink with simple components such as filter paper and transparency sheets to fabricate low-cost sensors that provide naked-eye monitoring of UVR, even at low doses typically encountered during solar exposure. Importantly, the diverse UV tolerance of different skin colors demands personalized sensors. In this spirit, we demonstrate the customized design of robust real-time solar UV dosimeters to meet the specific need of different skin phototypes. These spectrally-selective UV sensors offer remarkable potential in managing the impact of UVR in our day-to-day life.

Oxygen-deficient photostable Cu2O for enhanced visible light photocatalytic activity.

Oxygen vacancies in inorganic semiconductors play an important role in reducing electron-hole recombination, which may have important implications in photocatalysis. Cuprous oxide (Cu2O), a visible light active p-type semiconductor, is a promising photocatalyst. However, the synthesis of photostable Cu2O enriched with oxygen defects remains a challenge. We report a simple method for the gram-scale synthesis of highly photostable Cu2O nanoparticles by the hydrolysis of a Cu(i)-triethylamine [Cu(i)-TEA] complex at low temperature. The oxygen vacancies in these Cu2O nanoparticles led to a significant increase in the lifetimes of photogenerated charge carriers upon excitation with visible light. This, in combination with a suitable energy band structure, allowed Cu2O nanoparticles to exhibit outstanding photoactivity in visible light through the generation of electron-mediated hydroxyl (OH˙) radicals. This study highlights the significance of oxygen defects in enhancing the photocatalytic performance of promising semiconductor photocatalysts.

Nanowire Morphology of Mono- and Bidoped α-MnO2 Catalysts for Remarkable Enhancement in Soot Oxidation.

In the present work, nanowire morphologies of α-MnO2, cobalt monodoped α-MnO2, Cu and Co bidoped α-MnO2, and Ni and Co bidoped α-MnO2 samples were prepared by a facile hydrothermal synthesis. The structural, morphological, surface, and redox properties of all the as-prepared samples were investigated by various characterization techniques, namely, scanning electron microscopy (SEM), transmission and high resolution electron microscopy (TEM and HR-TEM), powder X-ray diffraction (XRD), N2 sorption surface area measurements, X-ray photoelectron spectroscopy (XPS), hydrogen-temperature-programmed reduction (H2-TPR), and oxygen-temperature-programmed desorption (O2-TPD). The soot oxidation performance was found to be significantly improved via metal mono- and bidoping. In particular, Cu and Co bidoped α-MnO2 nanowires showed a remarkable improvement in soot oxidation performance, with its T50 (50% soot conversion) values of 279 and 431 °C under tight and loose contact conditions, respectively. The soot combustion activation energy for the Cu and Co bidoped MnO2 nanowires is 121 kJ/mol. The increased oxygen vacancies, greater number of active sites, facile redox behavior, and strong synergistic interaction were the key factors for the excellent catalytic activity. The longevity of Cu and Co bidoped α-MnO2 nanowires was analyzed, and it was found that the Cu/Co bidoped α-MnO2 nanowires were highly stable after five successive cycles and showed an insignificant decrease in soot oxidation activity. Furthermore, the HR-TEM analysis of a spent catalyst after five cycles indicated that the (310) crystal plane of α-MnO2 interacts with the soot particles; therefore, we can assume that more-reactive exposed surfaces positively affect the reaction of soot oxidation. Thus, the Cu and Co bidoped α-MnO2 nanowires provide promise as a highly effective alternative to precious metal based automotive catalysts.

Laying Waste to Mercury: Inexpensive Sorbents Made from Sulfur and Recycled Cooking Oils.

Mercury pollution threatens the environment and human health across the globe. This neurotoxic substance is encountered in artisanal gold mining, coal combustion, oil and gas refining, waste incineration, chloralkali plant operation, metallurgy, and areas of agriculture in which mercury-rich fungicides are used. Thousands of tonnes of mercury are emitted annually through these activities. With the Minamata Convention on Mercury entering force this year, increasing regulation of mercury pollution is imminent. It is therefore critical to provide inexpensive and scalable mercury sorbents. The research herein addresses this need by introducing low-cost mercury sorbents made solely from sulfur and unsaturated cooking oils. A porous version of the polymer was prepared by simply synthesising the polymer in the presence of a sodium chloride porogen. The resulting material is a rubber that captures liquid mercury metal, mercury vapour, inorganic mercury bound to organic matter, and highly toxic alkylmercury compounds. Mercury removal from air, water and soil was demonstrated. Because sulfur is a by-product of petroleum refining and spent cooking oils from the food industry are suitable starting materials, these mercury-capturing polymers can be synthesised entirely from waste and supplied on multi-kilogram scales. This study is therefore an advance in waste valorisation and environmental chemistry.

Co3O4@CeO2 hybrid flower-like microspheres: a strong synergistic peroxidase-mimicking artificial enzyme with high sensitivity for glucose detection.

In recent years, the development of artificial nanostructured enzymes has received enormous interest in nanobiotechnology due to their advantages over natural enzymes. In the present work, different amounts (5, 10, and 20 wt%) of Co3O4 nanoparticle decorated CeO2 hybrid flower-like microspheres (Co3O4@CeO2) have been investigated for peroxidase-like activity and it was found that 10 wt% of Co3O4@CeO2 exhibited excellent peroxidase-like activity for the catalytic oxidation of the 3,3',5,5'-tetramethylbenzidine (TMB) substrate in the presence of H2O2. The formation of more Ce3+ ions associated with the oxygen vacancies and a strong synergistic interaction between CeO2 and Co3O4 may be responsible for the enhanced peroxidase-like activity. Based on their peroxidase activity, Co3O4@CeO2 hybrid microspheres were used for the colourimetric detection of glucose. It was found that Co3O4@CeO2 hybrid microspheres showed a substantial enhancement in the detection selectivity. The limit of detection (LOD) was also improved with a limit as low as 1.9 µM. Thus, we believe that Co3O4@CeO2 hybrid flower-like microspheres with high peroxidase-like activity can be exploited for biosensing applications.

Fe-doped CeO2 nanorods for enhanced peroxidase-like activity and their application towards glucose detection.

The construction of highly efficient inorganic mimetic enzymes (nanozymes) is much needed to replace natural enzymes due to their instability and high cost. Recently, nanoscale CeO2 has been attracting significant interest due to its unique properties such as facile redox behaviour (Ce4+↔ Ce3+) and surface defects. In the present work, various amounts of Fe3+-doped CeO2 nanorods (NRs) (with 3, 6, 9, and 12% Fe doping) were synthesized using a facile hydrothermal method and investigated for peroxidase-like activity and glucose detection. The peroxidase-like activity results revealed that 6 at% doping is the optimal Fe doping level to demonstrate superior catalytic performance over un-doped and Fe3+-doped CeO2 NRs. Steady state kinetic analysis also confirms that the 6% Fe3+-doped CeO2 (6Fe/CeO2) NRs exhibited excellent catalytic performance towards 3,3',5,5'tetramethylbenzidine (TMB) oxidation with a Km and Vm of 0.176 mM and 8.6 × 10-8 M s-1, respectively, as compared to horseradish peroxidase (HRP) enzymes (0.434 mM and 10.0 × 10-8 M s-1). Typical colour reactions arising from the catalytic oxidation of the TMB substrate over 6Fe/CeO2 NRs with H2O2 have been utilized to establish a simple sensitive and selective colorimetric assay for the determination of glucose concentration in buffer, diluted fruit juices and foetal bovine serum samples. The superior catalytic performance of 6Fe/CeO2 NRs could be attributed to abundant surface defects, high surface area and pore volume, and preferential exposure of the highly reactive (110) planes.