Smart adsorbents for CO2 capture:Making strong adsorption sites respond to visible light

Due to the good controllability and high energy efficiency in adsorption processes,photoresponsive adsorbents are intriguing for CO2 capture.Nevertheless,most reported photoresponsive adsorbents are designed based on weak adsorption sites,regulating CO2 adsorption through structural change or steric hindrance.In addition,ultraviolet(UV)light is commonly involved in the regulation of adsorption capacity.Here we report for the first time the smart adsorbents for CO2 capture,which makes strong adsorption sites respond to visible(Vis)light.The adsorbents were fabricated by introducing primary amine and Dispersed Red 1(DR1,a kind of push-pull azobenzene that responds to Vis light rapidly)units to mesoporous silica,which act as strong adsorption sites and triggers,respectively.The primary amine sites make the adsorbents highly selective in the adsorption of CO2 over CH4.Without light irradiation,azobenzene is in the form of trans configuration,which leads to decreased electrostatic potential of primary amines and subsequently,exposure of active sites and liberal adsorption of CO2.Upon Vis-light irradiation,cis isomers are formed,which results in increased electrostatic potential of primary amines and subsequently shelter of active sites.Even on such strong adsorption sites,the alteration of CO2 adsorption capacity can reach 40%for the adsorbent with and without Vis-light irradiation.Moreover,the trans/cis isomerization of DR1 units can be triggered reversibly by Vis light.The present smart system endows adsorbents with selective adsorption capacity and avoids the employment of UV light,which is unlikely to be achieved by conventional photoresponsive adsorbents.

Adsorption Mechanism of Polycarboxylate-Based Superplasticizer in CFBC Ash-Portland Cement Paste

Circulating fluidized bed combustion （CFBC） ash exhibits the desirable pozzolanic activity which makes it a potential supplementary cementitious material to replace cement for concrete production. However, the high unburnt carbon content and porous surface structure of CFBC ash may adsorb water reducer and thereby significantly reduce the efficiency of water-reducing agents. The adsorption mechanism of polycarboxylate superplasticizer in CFBC ash-Portland cement paste was investigated by ultraviolet-visible spectrophotometer, and the conception of ＂invalid adsorption site＂ of CFBC ash was presented. The results show that the adsorption behavior of polycarboxylate superplasticizer in coal ash-Portland cement paste can be described by Langmuir isothermal adsorption equation. The adsorption capacity of CFBC ash-Portland cement paste is higher than that of pulverized coal combustion （PCC） fly ash-Portland cement paste. Moreover, the adsorption amount of polycarboxylate superplasticizer increases with the ratio of ash-to-cement in the paste. At last, the fluidity of CFBC ash-Portland cement paste is lower than that of the PCC fly ash paste. This work suggests that when CFBC ash is used as concrete admixture, the poor flowability of the cementitious system due to the high adsorption of water and water-reducing agent should be taken into consideration.

DFT Investigation of O_2 Adsorption on Si(001)-(2×2×1):H

A novel model was developed to theoretically evaluate the 02 adsorption on H-terminated Si（001）-（2×2×1） surface. The periodic boundary condition, the ultrasoft pseudopotentials technique based on density functional theory （DFT） with generalized gradient approxi,natior, （GGA） functional were applied in our ab initio calculations. By analyzing bonding energy oil site, the favourable adsorption site was determined. The calculations also predicted that the adsorption products should be Si=O and H2O. This theoretical study snpported the reaction mechanism provided by Kovalev et al, The results were also a base for further investigation of some more complex systems such as the oxida.tion on porous silicon surface.

Effects of Surface Defects on Adsorption of CO and Methyl Groups on Rutile TiO_(2)(110)

The interaction of reactants with catalysts has always been an important subject for catalytic reactions.As a promising catalyst with versatile applications,titania has been intensively studied for decades.In this work we have investigated the role of bridge bonded oxygen vacancy(O_(v))in methyl groups and carbon monoxide(CO)adsorption on rutile TiO_(2)(110)(R-TiO_(2)(110))with the temperature programmed desorption technique.The results show a clear different tendency of the desorption of methyl groups adsorbed on bridge bonded oxygen(O_(b)),and CO molecules on the five coordinate Ti^(4+)sites(Ti_(5c))as the Ovconcentration changes,suggesting that the surface defects may have crucial influence on the absorption of species on different sites of R-TiO_(2)(110).

A Frequency-Response Study on Sorption of Thiophene and Benzene on NiY Zeolite

The adsorption behavior of thiophene and benzene on NiY zeolite has been investigated by the frequency response(FR) method.The FR spectra of thiophene and benzene on NiY zeolite were recorded at 302-335 K in a pressure range of 26.6-266 Pa.The results showed that adsorption was found to be the rate-controlling process for the thiophene/NiY zeolite system,and there were two different adsorption processes.Two kinds of adsorption models have been proposed,namely:the S-M interaction(low frequency adsorption) and the π-complexation(high frequency adsorption).High frequency adsorption obeyed the Langmuir model.By combining the FR method and Langmuir model,the adsorption site of high frequency adsorption process at 302 K and 335 K was 3.172 mmol/g and 2.974 mmol/g,respectively,and on the combined adsorption isotherms,the adsorption site of the low frequency adsorption process at 302 K and 335 K was 0.308 mmol/gand 0.436 mmol/g,respectively.The low frequency adsorption process(S-M interaction) was the main adsorption process.The diffusion process was the rate-controlling process for the benzene-NiY zeolite system.

Construction of robust and durable Cu_(2)Se-V_(2)O_(5) nanosheet electrocatalyst for alkaline oxygen evolution reaction

Reducing the production costs of clean energy carriers such as hydrogen through scalable water electrolysis is a potential solution for advancing the hydrogen economy.Among the various material candidates,our group demonstrated transition-metal-based materials with tunable electronic characteristics,various phases,and earth-abundance.Herein,electrochemical water oxidation using Cu_(2)Se-V_(2)O_(5) as a non-precious metallic electrocatalyst via a hydrothermal approach is reported.The water-splitting performance of all the fabricated electrocatalysts was evaluated after direct growth on a stainless-steel substrate.The electrochemically tuned Cu_(2)Se-V_(2)O_(5) catalyst exhibited a reduced overpotential of 128 mV and provided a reduced Tafel slope of 57 mV·dec^(−1) to meet the maximum current density of 250 mA·cm^(−2).The optimized strategy for interfacial coupling of the fabricated Cu_(2)Se-V_(2)O_(5) catalyst resulted in a porous structure with accessible active sites,which enabled adsorption of the intermediates and afforded an effective charge transfer rate for promoting the oxygen evolution reaction.Furthermore,the combined effect of the catalyst components provided long-term stability for over 110 h in an alkaline solution,which makes the catalyst promising for large-scale practical applications.The aforementioned advantages of the composite catalyst overcome the limitations of low conductivity,agglomeration,and poor stability of the pure catalysts(Cu2Se and V2O5).

Morphology and photocatalytic tetracycline degradation of g-C_(3)N_(4) optimized by the coal gangue

Coal gangue(CG),a solid waste from coal mining and processing,has raised concerns about its environmental impact.Graphitic carbon nitride(g-C_(3)N_(4))is promising for photocatalytic decomposition of organic pollutants,but its performance is hampered by its inherent defects.In this study,the compound of coal gangue and g-C_(3)N_(4)was formed by in-situ loading g-C_(3)N_(4)on the surface of coal gangue.After recombination,the morphology of g-C_(3)N_(4)changes from block structure to tremella nanosheet.This change not only increases the specific surface area of g-C_(3)N_(4),but also broadens the light absorption spectrum of g-C_(3)N_(4).Compared with original g-C_(3)N_(4),the photo-current of the complex in visible light is increased twice,and the tetracycline(TC)degradation rate is 2.1 times faster.The structure,optical properties,band structure,morphology and charge transfer mechanism of the composite were analyzed by a series of characterization techniques.It is found that coal gangue can promote the space charge transfer and separation of g-C_(3)N_(4),and the cyclic test compound has good activity stability.In this paper,a strategy of comprehensive utilization of coal gangue is proposed,which can not only reduce the envi-ronmental risk of coal gangue,but also provide carbon nitride(CN)based photocatalytic materials with superior photocatalytic properties.

Role of surface roughness in the magnesite flotation and its mechanism

Surface roughness has a significant influence on mineral flotation.The assisting effect of surface roughness on minerals flotation is extensively investigated from its physical properties(e.g.,the existing form of asperity and its size),however,the associated effect on mineral flotation based on the differences in surface chemical property caused by surface roughness has been rarely touched.With such a question in mind,in this study,we investigated the flotation recoveries of two batches of magnesite particles with varying degree of surface roughness produced by two different mills,and associated the flotation performances to their surface chemical properties(amount of adsorption sites for the collector)via a series of detections,including Scanning Electron Microscope-Energy Dispersive Spectrometry(SEM-EDS)observations,X-ray photoelectron spectroscopy(XPS)analysis,adsorption capacity tests,and contact angle measurements.Finally,we concluded that rougher magnesite particles could provide more active sites(Mg^(2+))for a larger capacity of sodium oleate(NaOL),thereby improving the hydrophobicity and floatability.

Sorbent Concentration Effect on Adsorption of Methyl Orange on Chitosan Beads in Aqueous Solutions

The adsorption of methyl orange（MO） on chitosan（CS） beads in aqueous solutions was investigated by a batch equilibration technique. Special emphasis was focused on the effect of sorbent concentration（cs） on the adsorp- tion equilibration of MO on CS beads. An obvious Cs-effect was observed in the adsorption equilibration, i.e., the ad- sorption amount（F） was declined with Cs increase. The classical Langmuir model adequately described the adsorption isotherm for each given cs. However, it could not be used to predict the cs-effect observed. The applicability of the Langmuir-SCA isotherm, a surface component activity（SCA） model equation, to fit the cs-effect data was examined. In the SCA model, the activity coefficient of sorbent surface sites, fsH2O, was assumed to be a function of cs due to the deviation of a real adsorption system from an ideal one, arisen from sorbent particle-particle interactions in real systems. The results show that the Langmuir-SCA isotherm could accurately describe the c：effect observed under the studied conditions. Furthermore, the effects of temperature（t）, pH, and electrolyte（NaNO3） concentration（ CNaNO3 ） on fsH2O were examined. The results show that fsH2O clearly decreased with increasing t（20-35℃） and pH（5-8）, but no obvious change in fsH2O was observed as CNaNO3 varied in a range 0.001-0.010 mol/L. These results give a better understanding of the cs-effect.