Adsorption-desorption Equilibrium Research Articles

Spectroelectrochemical determination of the conduction band level of mesoporous titanium dioxide semiconductor in diverse reaction media

AbstractThe conduction band edge (ECB) energy levels of a mesoporous TiO2 film were investigated in aprotic dimethylformamide (DMF) and aqueous media to explore the influence of various proton additives and electron donors. Spectroelectrolysis (SE) technique was employed to measure the ECB in non‐aqueous solvents, revealing a significantly negative ECB in dry non‐aqueous solvents compared to values obtained in aqueous solvents. In non‐aqueous DMF, the ECB of TiO2 was found to be highly dependent on the proton‐donating additive due to the establishment of a proton adsorption–desorption equilibrium, reaching –(1.42–1.94) V versus SCE. The introduction of a well‐known electron donor, 1,3‐dimethyl‐2‐phenyl‐1,3‐dihydrobenzimidazole (BIH) led to a slight positive shift in the TiO2 ECB, indicating that the electron donor contributes to the to the CB energetics of the mesoporous TiO2 films. Under aqueous conditions and in the presence of various electron donors (TEA, TEOA, ascorbic acid, EDTA•2Na, and sodium ascorbate), the proton‐donating/accepting capacity of the additive significantly influenced the pH of the aqueous solvent, causing changes in the TiO2 ECB across the electrolyte solution. This study emphasizes the crucial role of proton additives and electron donors in influencing the CB energetics of mesoporous TiO2 electrodes and aims to determine the extent to which the ECB of TiO2 can shift as a result of the adsorption and intercalation of protons on its surface. The findings obtained herein contribute to the understanding of the energy efficiency of TiO2‐mediated photocatalytic systems in various solvent environments.

Surface coverage ratio of contaminated Taylor bubbles in a square microchannel

Experiments on contaminated Taylor flows in a microchannel were carried out to investigate the surface coverage ratio for different surfactant properties. Nitrogen and water were used for the gas and liquid phases, respectively. Triton X-100, sodium dodecyl sulfate (SDS) of 90% purity and SDS of 99% purity were used as surfactant. The cross section of the microchannel was square and its width was 200μm. The gas and liquid volumetric fluxes were 0.54 and 0.50 m/s, respectively. Taylor flows were formed by mixing the two phases at the T-junction. Shapes of Taylor bubbles were observed using a microscope and a high-speed video camera. The liquid film thickness changed in the film region, demonstrating that a steep gradient of the interfacial surfactant concentration was formed there. The interface was therefore separated into the clean interface region and the immobilized region by detecting the change in the liquid film thickness. The surface coverage ratio estimated from bubble shapes agreed with that measured from the reduction in the bulk concentration due to surfactant separation by bubbles. The surface coverage ratio increased with increasing the bulk concentration and the increasing rate was smaller than that for the adsorption–desorption equilibrium because of the presence of interfacial advection. The data, however, could be fitted by modifying the functional form for the ad-desorption equilibrium. The bulk concentration normalized by the concentration for the breakdown of the logarithmic relation between the surface tension and the concentration given by the isotherm worked for correlating the surface coverage ratio for the three different surfactants, which can be understood from the order of magnitude of the Marangoni stress.

Ni, Co-Embedded MOF-Derived N-Doped Bimetallic Porous Carbon for Adsorption-Photocatalytic Degradation of Organic Dyes and Antibiotics.

An efficient protocol for photocatalytic degradation of organic dyes and antibiotics has been successfully established via MOF-derived (MOF = metal-organic framework) Ni, Co-embedded N-doped bimetallic porous carbon nanocomposites (NiCo/NC). Such a NiCo/NC nanocomposite features well-distributed structures, suitable specific surface areas, and more active sites determined by various characterization analyses. The catalyst exhibits higher photocatalytic performance and stability toward the liquid-phase degradation of methylene blue (MB) under visible light irradiation for 60 min, after the adsorption-desorption equilibrium and the thorough degradation into H2O and CO2. Radical quenching experiments further confirmed the dominant effect of electron holes h+ and superoxide radical anions ·O2- for the MB photodegradation process. NiCo/NC was also appropriate for the degradation of Rhodamine B, methyl orange, tetracycline hydrochloride, and norfloxacin. Moreover, NiCo/NC is robust, and its photocatalytic activity is basically maintained after 8 cycles. This work is expected to provide additional information for the design of MOF-derived carbon material with more excellent properties and lay the foundation for further industrial applications.

Photocatalytic Degradation of Rhodamine B under UV Light Catalyzed by Alpha Titanium Phosphate and Metal Modified Titanium Phosphate

Wastewater management is a crucial issue in most emergent nations with ever-growing global industrialization. From textiles to food, mankind uses dyes and pigments which pose a threat to the environment due to organic non-biodegradable dyes contained in wastewater. Rhodamine B (RhB) is a conventional colorant in many industries producing a large amount of dye effluent, thus becoming a serious threat to the environment as well as human health. Additionally, RhB is dangerous even at extremely low quantities, making treatment of the RhB effluent more essential. Even though TiO2 is considered as the best photocatalyst to remove many organic pollutants, acceptable alternatives are needed due to being uneconomical in large-scale usage. Synthesis of titanium bismonohydrogen orthophosphate (α-TiP) can be achieved by refluxing ilmenite with phosphoric acid via a previously reported novel method. Solid state reactions of α-TiP and oxides of Co and Cu at 800° C result in various metal titanium phosphates (M-TiP) with unique colors. XRD, FTIR, and Diffuse reflectance UV-vis techniques were used for characterization of the obtained solids. Bandgap of α-TiP changed with the modification of different transition metal cations lowering bandgap from 4.01eV (α-TiP) to 3.57 eV (Cu-TiP). Aqueous RhB degradation under UV irradiation was used to investigate the photocatalytic abilities of these catalysts. For that 0.2 g sample of catalyst was added to a solution that contained 200 mL of a 5 mg L-1 Rh B which was kept for 15 mins in dark to reach adsorption-desorption equilibrium before exposing the sample to UV irradiation for 3 h. A clear enhancement of photocatalytic activity was observed from using Co- TiP as the catalyst, which only took around 80 min to remove almost all Rh B contained in the sample compared to α-TiP which took close to 3 h to become colorless. It was in alignment with spectrometer results where a clear reduction of intensity can be seen in wavelength at 552 nm. Photocatalytic activities of these catalysts decreased in the following order: Co-TiP>α-TiP>Cu-TiP. The Co-modified TiP showed degradation of 99.5% after 3 h of UV irradiation and pseudo first- order kinetics were followed by the degradation. 
 Keywords: Titanium Phosphate, Photocatalyst, Rhodamine B, Wastewater management

Interchangeable effect of polyols-based zeolite on the separation of CO2, CH4, and N2 gases

The adsorptive separation process for CO2/CH4 and CH4/N2 gas separation has commercial potential, in biogas, Coalbed Methane process etc. although it remains to strive due to the absence of effective adsorbents. Zeolite NaY was used in this study due to its uniform pore structures, surface properties, and potential gas separation adsorbent. Zeolite NaY was modified by polyether polyols (PEPO) to get an adsorbent for selective separation of CO2/CH4 and CH4/N2 gas mixtures. The PXRD, FT-IR, GPC, 1H NMR, TEM, and surface area analysis were used to characterize the PEPO and PEPO-modified zeolite. The single component equilibrium adsorption desorption isotherms with PEPO modified NaY zeolites and NaY zeolite for CO2, CH4 and N2 were measured at 298, 313, and 328 K and up to 5 bar pressure. The isotherm data of CO2, CH4 and N2 were fitted in Dual Site Langmuir equations, and adsorption selectivity of CO2/CH4 and CH4/N2 gas mixtures was predicted using Ideal Adsorbed Solution Theory (IAST) method for 90:10, 50:50 (vol/vol) CH4/N2 and 80:20, 50:50 (vol/vol) CO2/CH4 feed gas mixtures representing coal bed methane gas composition and pressure conditions. The high surface area and hydroxyl groups in PEPO-modified NaY enhanced selectivity for CO2/CH4 and CH4/N2 gas separation. The selectivity predicted by the IAST method were 106.12 and 95.34 for 0.5 % PEPO-NaY (80:20 v/v and 50:50 v/v) for CO2/CH4 and 3.95 and 3.52 for 2 % PEPO-NaY (90:10 v/v and 50:50 v/v) for CH4/N2 at 298 K up to 5 bar respectively.

Anti-Arrhenius passage of gaseous molecules through nanoporous two-dimensional membranes.

The passage of molecules through membranes is known to follow an Arrhenius-like kinetics, i.e. the flux is accelerated upon heating and vice versa. There exist though stepwise processes whose rates can decrease with temperature if, for example, adsorbed intermediates are involved. In this study, we perform temperature-variable permeation experiments in the range from -50 to +50 °C and observe anti-Arrhenius behaviour of water and ammonia permeating in two-dimensional freestanding carbon nanomembranes (CNMs). The permeation rate of water vapour is found to decrease many-fold with warming, while the passage of ammonia molecules strongly increases when the membrane is cooled down to the dew point. Liquefaction of isobutylene shows no enhancement for its transmembrane flux which is consistent with the material's pore architecture. The effects are described by the Clausius-Clapeyron relationship and highlight the key role of gas-surface interactions in two-dimensional membranes.

Enhanced catalytic reductive hydrogenation of an organic dye by Ag decorated graphitic carbon nitride modified MCM-41.

Utilization of efficient, stable and reusable catalysts for wastewater treatment and catalytic elimination of toxic pollutants is a challenge among researchers. This present work shows the synthesis of high-surface-activity Ag nanoparticle decorated gC3N4 modified MCM-41 and its efficiency towards catalytic hydrogenation of organic dye in the presence of reducing agent NaBH4. The proposed mechanism is based on the transfer of H+ and 2e- between the dye and the catalyst. Adsorption of dye stuff on the catalyst is a rate-determining step and is accelerated by the MCM-41 support which enhances the surface area. The catalytic efficiency and optimum time requirement were examined through the adsorption-desorption equilibrium, pseudo-first-order reaction kinetic model for the dye. The result obtained was 98% catalytic efficiency followed by the catalytic hydrogenation reaction.

Simulation study of drag force characteristics of nanoparticles in transition regime

Transport properties of nanoparticles in gases have many practical applications, such as aerosol science, combustion, and micro- and nano-scale fabrication. A nanoparticle moving in a fluid is expected to experience a drag force, which determines the transport property of the particle. According to the Einstein relationship, the diffusion coefficient of a particle is inversely proportional to the drag force coefficient. However, in the transition regime, it is usually difficult to evaluate the drag force of suspended particles. A typical method is to extend the asymptotic solution of the free molecular or continuum limit to the transition regime. According to the gas kinetic theory, Li and Wang proposed a theoretical expression for drag force on nanoparticles in the free molecular regime, which is then extended to the entire range of Knudsen number following a semi-empirical approach [Li Z G, Wang H 2003 <i>Phys. Rev. E</i> <b>68</b> 061207]. For nanoparticles, it is necessary to verify the theoretical predictions since the gas-particle non-rigid-body interactions must be taken into account. In this work, the drag force on nanoparticle in the transition regime is investigated by using molecular dynamics (MD) simulation. To evaluate the drag force, a harmonic potential is used to the nanoparticle to constrain its Brownian motion in our MD simulation. In the steady state, the drag force can be obtained by the balance between the drag force and harmonic force. It is found that the gas-particle non-rigid-body interaction has a significant influence on the drag force of nanoparticle. For weak gas-solid coupling, the MD simulation results can be in good agreement with the prediction of Li-Wang theory. However, for strong coupling, there exists significant discrepancy between the MD simulation results and the theoretical results. Due to the gas-solid intermolecular interactions, gas molecules can be adsorbed on the nanoparticle surface, and after a time period, they may be re-emitted from the surface when they gain sufficient kinetic energy. Therefore, an adsorption-desorption equilibrium and an adsorption layer can be established on the particle surface. The adsorption layer enlarges the collision cross-sectional area and enhances the momentum transfer between gas molecules and the particle, and thus the drag force increases. This can explain the inconsistencies between the theoretical results and MD simulations. In this work, we introduce an adsorption ratio to evaluate the thickness of the adsorption layer. Then, the effective particle radius can be defined by the sum of particle radius and the thickness of the adsorption layer. By using the effective particle radius, the simulation values are in very good agreement with the theoretical predictions. The results of this work provide insights into the applications of nanoparticles in aerosol science.

Theoretical predictions of properties and adsorption behaviour of group 1 and 2 elements, including elements 119 and 120, on hydroxylated quartz surfaces from periodic DFT calculations

Adsorption properties of group 1 and 2 elements Cs, Fr and E119 and Ba, Sr and E120, respectively, and of group 1 hydrides and hydroxides on hydroxylated quartz surfaces were calculated using a periodic relativistic DFT approach. The results show that all the considered group 1 and 2 elements should adsorb rather moderately on the quartz surfaces, with E119 and E120 most weakly, due to the strong relativistic stabilisation and contraction of the 8s atomic orbital. This means that E119 and E120 should have a deposition peak in the quartz chromatography column with a temperature gradient from room temperature to far below zero in the sequence Cs/Ba > Fr/Ra > E119/E120. For group 1 element MH and MOH, the adsorption energies are high, so that the adsorption–desorption equilibrium should be reached at very high temperatures, with the following trend in the adsorption strength MH > MOH >> M. Relativistic periodic DFT calculations of the adsorption properties of group 1 and 2 elements, including elements 119 and 120, and of their hydrides and hydroxides, on the hydroxylated quartz surfaces.

An Adsorption-Desorption Heat Engine for Power Generation from Waste Heat

According to the United States Department of Energy, waste heat recovery would allow up to a 20% reduction in greenhouse gases (GHG) emission. Most of the waste energy is discharged as a low-grade heat at temperatures less than 250°C. Therefore, the development of new technologies and the enhancement of existing ones to convert low-grade heat into electrical or mechanical energy are of great importance. The working principle of adsorption-desorption heat pumps with cyclic switching between adsorption and desorption is adapted in the proposed heat engine to generate electrical power from low-temperature heat. Thermodynamic analysis of the heat engine cycle is carried out for the pair adsorbant-adsorbent: CO<sub>2</sub>-activated carbon. Its efficiencies are calculated accepting the ideal gas law and an adsorption-desorption equilibrium at the key points of the cycle. The cycle consists of two isochores and two isotherms like the Stirling engine, but at the same temperature range and without heat regeneration, its thermal efficiency (work per heat supplied) can reach 11.3% vs. 5.0% and specific work 50.7 vs. 3.55 in the latter. The proposed unit has thermal efficiency in the range of Organic Rankine Cycle units and can be utilized in small-scale applications up to 40kWe, where manufacturing cost of turbines or expanders for ORCs increases dramatically. Accounting for quality (temperature) of utilized heat, the proposed cycle’s exergy efficiency, <em>ζ<sub>ex</sub></em> = 34.5% approaches that of water-steam Rankine cycles utilizing natural gas or coal combustion.

The persistence of smoke VOCs indoors: Partitioning, surface cleaning, and air cleaning in a smoke-contaminated house.

Wildfires are increasing in frequency, raising concerns that smoke can permeate indoor environments and expose people to chemical air contaminants. To study smoke transformations in indoor environments and evaluate mitigation strategies, we added smoke to a test house. Many volatile organic compounds (VOCs) persisted days following the smoke injection, providing a longer-term exposure pathway for humans. Two time scales control smoke VOC partitioning: a faster one (1.0 to 5.2 hours) that describes the time to reach equilibrium between adsorption and desorption processes and a slower one (4.8 to 21.2 hours) that describes the time for indoor ventilation to overtake adsorption-desorption equilibria in controlling the air concentration. These rates imply that vapor pressure controls partitioning behavior and that house ventilation plays a minor role in removing smoke VOCs. However, surface cleaning activities (vacuuming, mopping, and dusting) physically removed surface reservoirs and thus reduced indoor smoke VOC concentrations more effectively than portable air cleaners and more persistently than window opening.

Design and Synthesis of Fluorinated Quantum Dots for Efficient and Stable 0D/3D Perovskite Solar Cells

AbstractDimensionality engineering involving the low‐dimensional and 3D perovskites has been demonstrated as an efficient promising strategy to modulate interfacial energy loss as well as instability in perovskite solar cells (PSCs). Herein, the use of fluorinated Cesium Lead Iodide (CsPbI3) perovskite quantum dot (PQD) is first reported as interface modification layer for PSCs. The binding between the CsPbI3 PQD surface and native oleic acid (OLA)/oleylamine (OAm) ligands is governed by a dynamic adsorption–desorption equilibrium. Perfluorooctanoic acid (PFA) with stronger binding affinity and more hydrophobic nature is explored to partially replace OLA to prepare the fluorinated ligand capped CsPbI3 PQDs (F‐CsPbI3). Through optimization of the addition of PFA during hot‐injection synthesis, the in situ treated F‐CsPbI3 PQDs display reduced surface defect states, higher photoluminescence quantum yields together with improved stability. Subsequently, both CsPbI3 and F‐CsPbI3 PQDs are utilized as interface engineering layer in PSCs, delivering the best efficiency values of 21.99% and 23.42%, respectively, which is significantly enhanced compared to the control device (20.37%). More importantly, benefiting from its more hydrophobic properties, the F‐CsPbI3 PQD treated device exhibits excellent ambient storage stability (25 °C, relative humidity: 35–45%), retaining over 80% of its initial efficiency after 1500 h aging.

Results of modelling the effect of temperature on the thickness of the surfactants layer

Problem. Earthmoving machines operate under high loads, so their tribo-joints periodically operate under unsteady load conditions, which leads to their increased wear and, as a result, a rapid decrease in the residual service life of the units and the reliability of the machines in general. Under unsteady load conditions, friction in the joints of hydraulic drive elements occurs under the boundary lubrication regime. This lubrication mode occurs at high contact loads, high temperatures in the contact zone, and relatively low sliding speeds of the mating surfaces. The combination of boundary lubrication and high dynamic loads often leads to partial destruction of the boundary layer. This leads to direct contact of individual micro-irregularities of the friction surfaces, which is accompanied by a wear process. Hence the importance of the quality of both the parameters of the surface layer of friction surfaces and the parameters of the applied lubricant (oils, working fluids) on the strength and wear resistance of hydraulic drive elements. Goal. The aim of this work is to determine the effect of temperature and radius of curvature of a microroughness on the thickness of the layer of surface-active substances adsorbed on it. Methodology. The solution of the tasks involved the formation of a model of adsorption-desorption equilibrium in the system "working fluid - micron-surface", taking into account the ambient temperature, and its application to determine the dependence of the thickness of the adsorbed surfactant layer under conditions of temperature change. Results. The thickness of the adsorption layer depends mainly on the size of the adsorbing surface field and the energy of thermal vibrations of molecules. It decreases with increasing PP and increases with increasing radius of curvature of the micron roughness. The change in the thickness of the adsorption layer of surfactant molecules on the surface of the micron roughness with a change in the temperature of the RS is not uniform. With an increase in the PP temperature within 300...400 K, the thickness of the adsorption layer of surfactant molecules on the surface of the micron roughness decreases by ~24 %. With an increase in the temperature of the PP in the range of 400...450 K, the thickness of the adsorption layer of surfactant molecules on the surface of the microroughness decreases by ~76 %. The formation of a surfactant adsorption layer on the surface of the microroughness at a temperature above 443 K stops. Originality. A model of the formation of a surfactant adsorption layer on the surface of a separate microroughness on the basis of adsorption-desorption equilibrium in the system "working fluid - microroughness surface" was proposed, taking into account the ambient temperature, which allows us to analyse the nature of the temperature effect on the thickness of the adsorbed surfactant layer. Practical value. The use of the proposed mathematical model makes it possible to estimate the parameter of the surfactant adsorption layer on the surfaces of microroughnesses and rough friction surfaces based on the ambient temperature and the geometry of individual microroughnesses.

Dynamics of Adsorbed CO Molecules on the TiO2 Surface under UV Irradiation

In this work, the UV-stimulated processes in the TiO2–COg system were explored by in situ FTIR spectroscopy and photoelectron spectroscopy. Kinetic dependences of the total band intensity for adsorbed CO and background absorption, as well as the positions of the Fermi level in TiO2 before, during, and after UV irradiation of the system, were analyzed and compared. The observed reversible shift in the adsorption–desorption equilibrium was explained by changing the electronic state of the photocatalyst under UV irradiation. The proposed mechanism of photostimulated CO adsorption and CO re-adsorption in the TiO2–COg system is described in detail. A deflection of reversibility of molecular photodesorption–re-adsorption dynamics is caused by the side reaction of CO photooxidation and the formation of strongly bound surface carbonates.

Cu surface doped TiO2: Constructing Cu single-atoms active sites and broadening the photo-response range for efficient photocatalytic hydrogen production

Photocatalysts loaded with suitable metal single atoms (SAs) have high catalytic activity due to the maximum exposure, which have excellent potential for photocatalytic hydrogen production. However, it cannot regulate the bandgap of support if the metal SAs are only exposed on the surface. Herein, combining the high activity of SAs with the bandgap regulation of doping, we proposed a metal surface doping strategy to construct Cu single-atoms TiO2 (CuSAs-TiO2). The surface anchored Cu atoms can effectively capture photogenerated electrons to reduce H intermediates, while the underneath doped Cu atoms can reduce the bandgap of TiO2 to broaden the photo-response range and improve the photoelectric response rate. Under the irradiation of light with wavelengths of 365, 385 and 420 nm, the apparent quantum efficiencies are all zero for pure TiO2, while that of the optimal CuSAs-TiO2 are 6.03%, 0.84% and 0.04%, respectively. Theoretical simulation is consistent with the experiments, and the interaction between the underneath doped Cu and the surface anchored Cu can improve the adsorption–desorption equilibrium of H intermediates and optimize hydrogen evolution kinetics. This work provides a feasible strategy for designing visible light-responsive single-atoms photocatalysts by combining the advantages of metal SAs and doping.

Bifunctional hierarchical NiCoP@FeNi LDH nanosheet array electrocatalyst for industrial-scale high-current-density water splitting

Aiming to design and prepare non-noble metal electrocatalysts for hydrogen production at high current density (HCD), NiCoP@FeNi LDH hierarchical nanosheets were deposited on nickel foam progressively using a hydrothermal-phosphorization-electrodeposition process. For hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), NiCoP@FeNi LDH/NF requires only 195 and 230 mV overpotentials to reach 1000 mA cm−2, respectively. For overall water splitting, only 1.70 V is required at 1000 mA cm−2. This is the largest value for non-noble metal-based electrocatalysts reported so far at HCD. The hierarchical structure exhibits good electron transport capability and the porous-macroporous structure enhances the gas release rate, resulting in enhanced hydrogen production at HCD. Especially, the synergistic effect of NiCoP and FeNi LDH contributes to the adsorption-desorption equilibrium of intermediate radicals during the reaction process and ultimately enhances the catalytic activity. This work provides useful direction for industrial-scale hydrogen production applications at HCD.

Effective and Efficient Porous CeO2 Adsorbent for Acid Orange 7 Adsorption.

A porous CeO2 was synthesized following the addition of guanidine carbonate to a Ce3+ aqueous solution, the subsequent addition of hydrogen peroxide and a final hydrothermal treatment. The optimal experimental parameters for the synthesis of porous CeO2, including the amounts of guanidine carbonate and hydrogen peroxide and the hydrothermal conditions, were determined by taking the adsorption efficiency of acid orange 7 (AO7) dye as the evaluation. A template-free hydrothermal strategy could avoid the use of soft or hard templates and the subsequent tedious procedures of eliminating templates, which aligned with the goals of energy conservation and emission reduction. Moreover, both the guanidine carbonate and hydrogen peroxide used in this work were accessible and eco-friendly raw materials. The porous CeO2 possessed rapid adsorption capacities for AO7 dye. When the initial concentration of AO7 was less than 130 mg/L, removal efficiencies greater than 90.0% were obtained, achieving a maximum value of 97.5% at [AO7] = 100 mg/L and [CeO2] = 2.0 g/L in the first 10 min of contact. Moreover, the adsorption-desorption equilibrium between the porous CeO2 adsorbent and the AO7 molecule was basically established within the first 30 min. The saturated adsorption amount of AO7 dye was 90.3 mg/g based on a Langmuir linear fitting of the experimental data. Moreover, the porous CeO2 could be recycled using a NaOH aqueous solution, and the adsorption efficiency of AO7 dye still remained above 92.5% after five cycles. This study provided an alternative porous adsorbent for the purification of dye wastewater, and a template-free hydrothermal strategy was developed to enable the design of CeO2-based catalysts or catalyst carriers.

Shape-specific MOF-derived Cu@Fe-NC with morphology-driven catalytic activity: Mimicking peroxidase for the fluorescent- colorimetric immunosignage of ochratoxin.

Ochratoxin A (OTA), which has strong hepatotoxicity and nephrotoxicity, can accumulate in the human body through the food chain; thus, the selective and effective detection of OTA is urgently required for food security. Nanozymes with hyperfine size and shape control have attracted attention because of their controllable structure and intrinsic activity. Herein, CuFe-bimetal coordinated N-doped carbon (Cu@Fe-NC) with morphology-driven peroxidase-mimicking activity was synthesized using Cu2O with specific polygonal cubes and fully exposed {111} crystalline facets as the template to produce a CuFe-bimetallic metal organic framework (MOF) and further treating CuFe-MOF with high-temperature pyrolysis. N-doping can confer electronegativity to exhibit high affinity, while the large surface area of the porous carbon support can facilitate rapid adsorption-desorption equilibrium. Using the peroxidase-mimicking Cu@Fe0.5-NC as a carrier, a versatile immunoassay for the detection of OTA was implemented based on the ratiometric fluorescence and the localized surface plasmon resonance peak shift, achieving a detection limit of 0.52ng/L in the range of 0.001-10μg/L. Therefore, the strategy of enhancing enzyme-mimicking activity using specific shapes and crystalline facets may open new avenues for food and environmental analysis.

Quantifying phosphorus levels in water columns equilibrated with sediment particles in shallow lakes: From algae/cyanobacteria-available phosphorus pools to pH response

Sediment phosphorus (P) release in shallow eutrophic lakes is a major contributor of P to algal blooms. This research proposes an innovative notion in which the P diffusive fluxes at the sediment-water interface (SWI) of shallow lakes are controlled by the P adsorption-desorption equilibria, with pH as the major regulating factor. The P equilibrium concentration (Ce) at SWI was conceptualized into a dependent variable responding to two factor-dependent variables, the algae/cyanobacteria-available P pools of the SWI and the pH in the water column, resulting in the empirical equation Ce(pH) = Cm/[1 + e−k(pH-pH1/2)]. Cm is the maximum P equilibrium concentration when all algae/cyanobacteria-available P in sediments is released, and the value relies on the thickness of the oxygen and pH transition layer that contains iron/aluminium (hydr)oxide-adsorbed P. The parameters in the empirical equation are accessible from P desorption tests conducted on a set of sediment samples with different P pollution levels. This research provides a quantitative approach for determining the sediment P criteria of shallow lakes, with sediment iron/aluminium (hydr)oxide-adsorbed P and water depth as two main indicators with ecological implications. A decrease in water depth would proportionally increase the P concentration at a similar sediment P releasing flux and increase algae/cyanobacteria-available P pools that are ready to equilibrate with the water column by increasing hydrodynamic disturbance of the SWI.

CuO Nanorods Immobilized Agar-Alginate Biopolymer: A Green Functional Material for Photocatalytic Degradation of Amaranth Dye.

The contamination of water is increasing day by day due to the increase of urbanization and population. Textile industries contribute to this by discarding their waste directly into water streams without proper treatment. A recent study explores the treatment potential of copper oxide nanorods (CuO NRs) synthesized on a green basis in the presence of a biopolymer matrix of agar (AA) and alginate (Alg), in terms of cost effectiveness and environmental impact. The synthesized bio nanocomposite (BNC) was characterized by using different instrumental techniques such as Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), ultra-violet spectroscopy (UV-Vis), scanning electron microscopy-energy dispersive X-ray-elemental analysis (SEM-EDX), transmission electron microscopy (TEM), selected area diffraction pattern (SAED) and X-ray photoelectron spectroscopy (XPS). The optical studies revealed that immobilization of CuO NRs with Alg-Agar biopolymer blend resulted in an increase in light absorption capacity by decreasing the energy bandgap from 2.53 eV to 2.37 eV. The bio nanocomposite was utilized as a photocatalyst for the degradation of amaranth (AN) dye from an aquatic environment under visible light irradiation. A statistical tool known as central composite design (CCD) associated with response surface methodology (RSM) was taken into consideration to evaluate the optimized values of process variables and their synergistic effect on photocatalytic efficiency. The optimized values of process variables were found to be irradiation time (45 min), AN concentration (80 ppm), catalyst dose (20 mg), and pH (4), resulting in 95.69% of dye degradation at 95% confidence level with desirability level 1. The rate of AN degradation was best defined by pseudo-first-order reaction based on the correlation coefficient value (R2 = 0.99) suggesting the establishment of adsorption-desorption equilibrium initially at the catalyst surface then photogenerated •O2- radicals interacting with AN molecule to mineralize them into small non-toxic entities like CO2, H2O. The material used has high efficiency and stability in photocatalytic degradation experiments up to four cycles of reusability.