Synergistic activation of smithsonite with copper-ammonium species for enhancing surface reactivity and xanthate adsorption

Copper ions(Cu^(2+))are usually added to activate the sulfidized surface of zinc oxide minerals to enhance xanthate attachment using sulfidization xanthate flotation technology.The adsorption of Cu^(2+)and xanthate on the sulfidized surface was investigated in various systems,and its effect on the surface hydrophobicity and flotation performance was revealed by multiple analytical methods and experiments.X-ray photoelectron spectroscopy(XPS)and time-of-flight secondary ion mass spectrometry(To F-SIMS)characterization demonstrated that the adsorption of Cu^(2+)on sulfidized smithsonite surfaces increased the active Cu—S content,regardless of treatment in any activation system.The sulfidized surface pretreated with NH_(4)^(+)-Cu^(2+)created favorable conditions for the adsorption of more Cu^(2+),significantly enhancing the smithsonite reactivity.Zeta potential determination,ultraviolet(UV)-visible spectroscopy,Fourier transform-infrared(FT-IR)measurements,and contact angle detection showed that xanthate was chemically adsorbed on the sulfidized surface,and its adsorption capacity in various systems was illustrated from qualitative and quantitative aspects.In comparison to the Na2S–Cu^(2+)and Cu^(2+)–Na2S–Cu^(2+)systems,xanthate exhibited a higher adsorption capacity on sulfidized smithsonite surfaces in NH_(4)^(+)-Cu^(2+)–Na2S–Cu^(2+)system.Hence,activation with Cu^(2+)–NH4+synergistic species prior to sulfidization significantly enhanced the mineral surface hydrophobicity,thereby increasing its flotation recovery.

Tuning the reactivity of TiO_(2)layer with uniform distribution of Sub-5 nm Fe_(2)O_(3)particles via in situ voltage-assisted oxidation for robust catalytic reduction

The trade-off between efficiency and stability has limited the application of TiO_(2)as a catalyst due to its poor surface reactivity.Here,we present a modification of a TiO_(2)layer with highly stable Sub-5 nm Fe_(2)O_(3)nanoparticles(NP)by modulating its structure-surface reactivity relationship to attain efficiency-stability balance via a voltage-assisted oxidation approach.In situ simultaneous oxidation of the Ti substrate and Fe precursor using high-energy plasma driven by high voltage resulted in uniform distribution of Fe_(2)O_(3)NP embedded within porous TiO_(2)layer.Comprehensive surface characterizations with density functional theory demonstrated an improved electronic transition in TiO_(2)due to the presence of surface defects from reactive oxygen species and possible charge transfer from Ti to Fe;it also unexpectedly increased the active site in the TiO_(2)layer due to uncoordinated electrons in Sub-5 nm Fe_(2)O_(3)NP/TiO_(2)catalyst,thereby enhancing the adsorption of chemical functional groups on the catalyst.This unique embedded structure exhibited remarkable improvement in reducing 4-nitrophenol to 4-aminophenol,achieving approximately 99%efficiency in 20 min without stability decay after 20 consecutive cycles,outperforming previously reported TiO_(2)-based catalysts.This finding proposes a modified-electrochemical strategy enabling facile construction of TiO_(2)with nanoscale oxides extandable to other metal oxide systems.

Exploring electronic-level principles how size reduction enhances nanomaterial surface reactivity through experimental probing and mathematical modeling

Size reduction can generally enhance the surface reactivity of inorganic nanomaterials.The origin of this nano-effect has been ascribed to ultrasmall size,large specific surface area,or abundant defects,but the most intrinsic electronic-level principles are still not fully understood yet.By combining experimental explorations and mathematical modeling,herein we propose an electronic-level model to reveal the physicochemical nature of size-dependent nanomaterial surface reactivity.Experimentally,we reveal that competitive redistribution of surface atomic orbitals from extended energy band states into localized surface chemical bonds is the critical electronic process of surface chemical interactions,using H_(2)O_(2)-TiO_(2)chemisorption as a model reaction.Theoretically,we define a concept,orbital potential(G),to describe the electronic feature determining the tendency of orbital redistribution,and deduce a mathematical model to reveal how size modulates surface reactivity.We expose the dual roles of size reduction in enhancing nanomaterial surface reactivity-inversely correlating to orbital potential and amplifying the effects of other structural factors on surface reactivity.

Ultrafast O_(2) activation by copper oxide for 2,4-dichlorophenol degradation:The size-dependent surface reactivity

This study demonstrated interesting ultrafast activation of molecular O_(2) by copper oxide(CuO)particles and very rapid elimination of aqueous 2,4-dichlo rophenol(2,4-DCP)within reaction time of 30 s.Electron paramagnetic resonance(EPR)characterization indicated that·OH,Cu^(3+),^1 O_(2) and O_(2)^·-were generated in the CuO/O_(2) systems,wherein O_(2)^·-would be the main reactive species responsible for 2,4-DCP degradation.It was further found that the catalytic ability of CuO for O_(2) activation was highly size dependent and nano-CuO was far reactive than micro-CuO.H2 temperature-programmed reduction(H2-TPR),X-ray photoelectron spectroscopy(XPS)and vibrating sample magnetometer(VSM)analyses revealed that both the quantity and the reactivity of the surface reaction sites(surface Cu+and O_(2))could determine the catalytic ability of CuO affecting efficient Cu^(+)-based molecular oxygen activation.Moreover,the O_(2) activation ability of CuO would depend on not only the dimension,but also crystalline factors,for example,the exposed facets.

Reactivity of Tourmaline by Quantum Chemical Calculations

ZnAb initio calculations on reactivity of tourmaline were performed using both Gaussian and density function theory discrete variation method （DFT-DVM）. The HF, B3LYP methods and basis sets STO-3G（3d,3p）,6-31G（3d,3p） and 6-311＋＋G（3df,3pd） were used in the calculations. The experimental results show energy value obtained from B3LYP and 6-31＋＋1G（3df,3pd） basis sets is more accurate than those from other methods. The highest occupied molecular orbital （HOMO） of the tourmaline cluster mainly consists of O atom of hydroxyl group with relative higher energy level, suggesting that chemical bond between those of electron acceptor and this site may readily form, indicating the higher reactivity of hydroxyl group. The lowest unoccupied molecular orbital （LUMO） of the tourmaline cluster are dominantly composed of Si, O of tetrahedron and Na with relative lower energy level, suggesting that these atoms may tend to form chemical bond with those of electron donor. The results also prove that the O atoms of the tourmaline cluster have stronger reactivity than other atoms.

Effect of reactive surface area of minerals on mineralization trapping of CO_2 in saline aquifers

The reactive surface area, an important parameter controlling mineral reactions, affects the amount of mineralization trapping of CO2 which affects the long-term CO2 storage. The effect of the reactive surface area on the mineralization trapping of CO2 was numerically simulated for CO2 storage in saline aquifers. Three kinds of minerals, including anorthite, calcite and kaolinite, are involved in the mineral reactions. This paper models the relationship between the specific surface area and the grain diameter of anorthite based on experimental data from literature （Brantley and Mellott, 2000）. When the reactive surface areas of anorthite and calcite decrease from 838 to 83.8 m^2/m^3, the percentage of mineralization trapping of CO： after 500 years decreases from 11.8% to 0.65%. The amount of dissolved anorthite and the amounts of precipitated kaolinite and calcite decrease significantly when the reactive surface areas ofanorthite and calcite decrease from 838 to 83.8 m2/m3. Calcite is initially dissolved in the brine and then precipitates during the geochemical reactions between CO2-H20 and the minerals. Different reactive surface areas of anorthite and calcite lead to different times from dissolution to precipitation. The pH of the brine decreases with decreasing reactive surface areas of anorthite and calcite which influences the acidity of the saline aquifer. The gas saturation between the upper and lower parts of the saline aquifer increases with decreasing reactive surface areas of anorthite and calcite. The mass density distribution of brine solution shows that the CO2^＋brine solution region increases with decreasing reactive surface areas ofanorthite and calcite.

Hydrogen Adsorption Mechanism of SiC Nanocones

Due to rapid depletion of fossil energy sources and increasing the environmental pollution through high fossil energy consumption, an alternative renewable and clean energy carrier as hydrogen is requested more investigations in order to get the optimal request by DOE. In this study, a deepest study on SiC nanocones is done including both of the geometrical and electronic properties of all possible five different disclination angles as a function of size using density functional (DFT) calculations at the B3LYP/6-31g level of theory. Then the hydrogen adsorption mechanism is investigated on three different sites: HS1 (above the first neighbor atom of the apex atoms), HS2 (above one atom of the apex atoms) and HS3 (above one atom far from the apex atoms). Our calculations show that the most candidate SiC nanocone structure for hydrogen storage is Si41N49H10-HS2-M1-Type 2 with disclination angle 300˚. In addition, our results indicate that the hydrogen adsorption induced the energy gap to decrease. Hence, these results indicate that the SiCNCs can be considered as a good candidate for hydrogen storage.

无监督机器学习揭示金属表面本征反应性

The reactivity of metal surfaces is a cornerstone concept in chemistry,as metals have long been used as catalysts to accelerate chemical reactions.Although fundamentally important,the reactivity of metal surfaces has hitherto not been explicitly defined.For example,in order to compare the activity of two metal surfaces,a particular probe adsorbate,such as O,H,or CO,has to be specified,as comparisons may vary from probe to probe.Here we report that the metal surfaces actually have their own intrinsic/eigen reactivity,independent of any probe adsorbate.By employing unsupervised machine learning algorithms,specifically,principal component analysis(PCA),two dominant eigenvectors emerged from the binding strength dataset formed by 10 commonly used probes on 48 typical metal surfaces.According to their chemical characteristics revealed by vector decomposition,these two eigenvectors can be defined as the covalent reactivity and the ionic reactivity,respectively.Whereas the ionic reactivity turns out to be related to the work function of the metal surface,the covalent reactivity cannot be indexed by simple physical properties,but appears to be roughly connected with the valence-electron number normalized density of states at the Fermi level.Our findings expose that the metal surface reactivity is essentially a two-dimensional vector rather than a scalar,opening new horizons for understanding interactions at the metal surface.

Lattice distortion releasing local surface strain on high-entropy alloys

High-entropy alloys(HEAs)have the potential to be a paradigm-shift for rational catalyst discovery but this new type of alloy requires a completely new approach to predict the surface reactivity.In addition to the ligand effect perturbing the surface–adsorbate bond,the random configuration of elements in the surface will also induce local strain effects due to the varying radii of neighboring atoms.Accurate modelling of HEA surface reactivity requires an estimate of this effect:To what degree is the adsorption of intermediates on these lattice distorted atomic environments affected by local strain?In this study,more than 3,500 density functional theory(DFT)calculated adsorption energies of*OH and*O adsorbed on the HEAs IrPdPtRhRu and AgAuCuPdPt are statistically analyzed with respect to the lattice constants of the alloys and the surfaces of each individual binding site.It is found that the inherent distortion of the lattice structure in HEAs releases the local strain effect on the adsorption energy as the atomic environment surrounding the binding atom(s)settles into a relaxed structure.This is even observed to be true for clusters of atoms of which the sizes deviate significantly from the atomic environment in which they are embedded.This elucidates an important aspect of binding site interaction with the neighboring atoms and thus constitutes a step towards a more accurate theoretical model of estimating the reactivity of HEA surfaces.

Light-switchable catalytic activity of Cu for oxygen reduction reaction

The surface reactivity of metals is fundamentally dependent on the local electronic structure generally tailored by atomic compositions and configurations during the synthesis.Herein,we demonstrate that Cu,which is inert for oxygen reduction reaction(ORR)due to the fully occupied d-orbital,could be activated by applying a visible-light irradiation at ambient temperature.The ORR current is increased to 3.3 times higher in the potential range between-0.1 and 0.4 V under the light of 400 mW·cm^-2,and the activity enhancement is proportional to the light intensity.Together with the help of the first-principle calculation,the remarkably enhanced electrocatalytic activity is expected to stem mainly from the decreased metal-adsorbate binding by photoexcita-tion.This finding provides an additional degree of freedom for controlling and manipulating the surface reactivity of metal catalysts besides materials strategy.

Activity and characteristics of ＂Oxygen-enriched＂ highly reactive absorbent for simultaneous flue gas desulfurization and denitrification

An ＂Oxygen-enriched＂ highly reactive absor- bent was prepared by mixing fly ash, lime and a small quantity of KMnO4 for simultaneous desulfiarization and denitrification. Removal of SO2 and NO simultaneously was carried out using this absorbent in a flue gas circulating fluidized bed （CFB）. The highest simultaneous removal efficiency, 94.5% of SO2 and 64.2% of NO, was achieved under the optimal experiment conditions. Scanning Electron Microscope （SEM） and Accessory X-ray Energy Spectrometer （EDX） were used to observe the surface characteristics of fly ash, lime, ＂Oxygen-enriched＂ highly reactive absorbent and the spent absorbent. An ion chromatograph （IC） and chemical analysis methods were used to determine the contents of sulfate, sulfite, nitrate and nitrite in the spent absorbents, the results showed that sulfate and nitrite were the main products for desulfurization and denitrification respectively. The mechanism of removing SO2 and NO simultaneously was proposed based on the analysis results of SEM, EDX, IC and the chemical analysis methods.

Screening performance of methane activation over atomically dispersed metal catalysts on defective boron nitride monolayers:A density functional theory study

Methane(CH_(4))controllable activation is the key process for CH_(4)upgrading,which is sensitive to the surface oxygen species.The high thermal conductivity and superb thermal stability of the hexagonal boron nitride(h-BN)sheet makes a single transition metal atom doped hexagonal boron nitride monolayer(TM-BN)possible to be a promising material for catalyzing methane partial oxidation.The performances of 24 TM-BNs for CH_(4)activation are systematically investigated during the CH_(4)oxidation by means of first-principles computation.The calculation results unravel the periodic va riation trends for the stability of TM-BN,the adsorption strength and the kind of O_(2)species,and the resulting CH_(4)activation performance on TM-BNs.The formed peroxide O_(2)^(2-)of which the O-O bond could be broken and O-anions are found to be reactive oxygen species for CH_(4)activation under the mild conditions.It is found that the redox potential of TM center,including its valence electron number,coordination environment,and the work function of TM-BN,is the underlying reason for the formation of different oxygen species and the resulting activity for CH_(4)oxidative dehydrogenation.