Large BET Area Research Articles

Construction of NiP/Ni(OH)2/Ag-ZIF photocatalyst with 2-methylimidazole framework for rapid removal of tetracycline

Tetracycline (TC) is a kind of antibiotic that is difficult to be degraded by photocatalysis due to its stable molecular structure, and no ideal photocatalyst has been developed so far, thus developing a photocatalyst that can efficiently remove TC remains a challenge. In this work, a novel ternary photocatalyst of NiP/Ni(OH)2/Ag-ZIF (NNA) with 2 −Methylimidazole framework was constructed via a facile liquid phase reaction, in which the NiP is amorphous with particle size of about 3–5 nm, the Ni(OH)2 is nano-flake crystal with a one-dimensional diameter of about 200 nm, and the Ag-ZIF is a octahedral crystal with a side length of 4 µm. The NiP nano particles covered on the surface of Ni(OH)2 nanosheeps to form NiP/Ni(OH)2 heterojunction with flower-like structure and large BET area of 393.11 m2 g−1, which was further assembled with Ag-ZIF to form NiP/Ni(OH)2/Ag-ZIF composite with double heterojunction. The as-constructed NNA shows high removal capacity for TC, while 10 mg NNA was added into 100 mL 60 mg/L TC solution and exposed in visible light for 60 min, 91.3% of TC was removed. Meanwhile, the NNA shows good stability and reusability, which is attribute to the reversible of adsorption and desorption process of NiP/Ni(OH)2 for TC and the excellent photo-corrosion resistance of Ag-ZIF. The radical trapping and electron spin resonance (ESR) tests manifested that the superoxide radical (O2-) and the hydroxyl radical (·OH) play the key role in the degradation of TC.

Directional dendritic gels constructed by binder-regulated freeze casting for enhanced uranium extraction from seawater

Directional microchannels can speed up the transportation of seawater in adsorbents, and the introduction of nanopores in the microchannels can enhance the specific surface area and endow the adsorbent with more adsorption sites, which are beneficial for improving the uranium adsorption ability. Herein, directional dendritic and hierarchical porous aerogels (DDH-PAO gels) were constructed by the binder-regulated freeze casting. The gels displayed directional dendritic channels and special honeycomb-like nanopores, which endowed the DDH-PAO gels with a rapid water permeation rate (0.74 s) and a large BET area. They exhibited good uranium adsorption capacities of 494.34 mg-U/g-Ads (in 16 ppm U-spiked simulated seawater) and 6.3 mg-U/g-Ads (in nonspiked natural seawater). The adsorption process can be observed by the naked eyes due to significant color changes before and after uranium adsorption. The uranium adsorption mechanism was analyzed by kinetic models and XPS spectra, and the role of regulators in microstructures formation was investigated by changing the amount of PVA. The directional microchannels, honeycomb-like nanopores, rapid water transportation rate, and high mechanical strength indicated that the DDH-PAO gels are promising for real uranium extraction from seawater.

Effects of the Acidic and Textural Properties of Y-Type Zeolites on the Synthesis of Pyridine and 3-Picoline from Acrolein and Ammonia

A set of Y-type zeolites with Si/Al atomic ratios between 7–45 were studied as catalysts in the aminocyclization reaction between acrolein and ammonia to produce pyridine and 3-picoline. The catalytic activity tests at 360 °C revealed that the acrolein conversion increased in the order Z45 < ZY34 < ZY7 < ZY17, in agreement with the increase of the total acidity per gram of catalyst. In all cases, pyridine bases and cracking products (acetaldehyde and formaldehyde) were detected in the outflow from the reactor. The total yield of pyridines was inversely proportional to the total acidity for the catalysts, which presented large surface areas and micro- and mesoporosity. The selectivity towards 3-picoline was favored when using catalysts with a Brønsted/Lewis acid sites ratio close to 1. The formation of pyridine occurred more selectively over Lewis acid sites than Brønsted acid sites. The deactivation tests showed that the time on stream of the catalysts depended on the textural properties of zeolites, i.e., large pore volume and large BET area, as evidenced by the deactivation rate constants and the characterization of the spent catalysts. The physicochemical properties of the catalysts were determined by XRD, UV-vis, and Raman spectroscopies, infrared spectroscopy with adsorbed pyridine, N2 physisorption, and SEM-EDXS. After the reaction, the spent catalysts were characterized by XRD, Raman spectroscopy, TGA, and SEM-EDXS, indicating that the uniform deposition of polyaromatic species on the catalyst surface and within the porous system resulted in the loss of activity.

Synergistic effects of rare earth doping and carbon quantum dots on BiOF/Bi2MoO6 heterojunctions for enhanced visible-near-infrared photocatalysis.

Herein, we designed and synthesized a series of rare earth doped BiOF/Bi2MoO6 heterojunctions. The doping locations of rare earth ions were altered to determine the influence on the visible and near-infrared photocatalytic activity of heterojunctions. It is experimentally and theoretically confirmed that doping with Tm3+/Yb3+ in one semiconductor of the heterojunction produces superior photocatalytic efficiency than doping in both semiconductors. In addition, the near infrared photocatalytic efficiency strongly relied on upconversion luminescence from the Re3+ doped semiconductor in the heterojunction. By further modifying with CQDs, the CQDs/BiOF:Tm3+,Yb3+/Bi2MoO6 sample shows excellent visible and near-infrared photocatalytic performance, with 90% degradation of RhB occurring in the first 20 min under visible irradiation. This can be attributed to the large BET area, efficient photoinduced carrier separation and the upconversion process of the composite. This research will provide a systematic solution for realizing full-spectrum responsive and highly efficient photocatalysis by combination of rare earth ion doping, quantum dot modification and Z-scheme heterojunctions.

Large-scale synthesis of visible light responsive ZnS by one-step molten salt method

It still remains a big challenge for the large-scale synthesis of visible light responsive ZnS. In this work, a simple one-step molten salt method is developed for large-scale synthesis of visible light responsive ZnS, in which the as-obtained sample at T oC is named as ST (T = 200, 300, 400, 500, 600 °C). The degradation reaction of Rhodamine B (RhB) is used to evaluate photocatalytic activity under visible light (λ ＞ 400 nm). Among the samples, S200 shows the highest visible light activity. Under visible light irradiation (λ ＞ 400 nm), 70% of RhB can be degraded by S200 after 90 min. Typically, the visible light activity of S200 is 28.2 times higher than that of S600. The higher activity of S200 is mainly attributed to more sulfur vacancies (VS), wider light absorption range, higher charge separation efficiency and larger BET area. Specifically, the BET area of S200 (44.4 m2 g−1) is 4.1 times higher than that of S600 (8.7 m2 g−1), thus S200 can provide more active sites. Meanwhile, the photocurrent for S200 is 6 times higher than that of S600, demonstrating that S200 has a higher charge separation efficiency mainly caused by more surface VS. Density functional theory (DFT) calculation further demonstrates that VS is favorable thermodynamically for the adsorptions of O2 and H2O, which benefits the generation of •OH and •O2– active species, leading to an improved activity. After three cycles of RhB degradation, S200 shows outstanding stability with 95% visible-light activity remained. The molten salt method is simple and productive, which can be used for large-scale synthesis of photocatalysts in practice.

In situ grown Co3O4 nanosheets in the interlayer space of g-C3N4 for efficient removal of Hg0 from flue gas

Hg0 adsorption with sorbents is a widely used way to remove Hg0 from coal fire flue gas. The adsorption efficiency and capacity are limited by the activation and number of the surface adsorption sites. In the present work, a series of composite sorbents with nanosheet structure were successfully synthesized by in situ growth of Co3O4 nanosheets in the interlayer space of g-C3N4. The effects of the mass ratio of Co3O4/g-C3N4 on sorbent physicochemical properties were comprehensively studied. Characterization results show that, when the mass ratio of Co3O4/g-C3N4 is 20%, the corresponding sorbent of 20%Co3O4/NS-g-C3N4 has well dispersion of Co3O4 nanosheets in g-C3N4 interlayer (SEM and TEM) and a relatively large BET area (BET). It results in a larger amount of surface chemisorbed oxygen which can react with Hg0 forming HgO. Furthermore, the strong interaction between Co3O4 and g-C3N4 make electron transfer from g-C3N4 to Co3O4 improving oxygen activation. Therefore, 20%Co3O4/NS-g-C3N4 has a higher Hg0 removal efficiency of 97% at 250 °C and it maintains above 80% even after 70 h test. XPS, FTIR and Hg0 desorption experiment results confirm that the adsorbed Hg mainly stays in the form of HgO and a probable adsorption mechanism is deduced by these results.

Morphology-Controllable Graphene-Modified Cu-Benzene-1,3,5 Tricarboxylic Acid Composites for Volatile Organic Compounds and CO2 Adsorption Property

Volatile organic compounds (VOCs) are the one kind of pollution, which lead to the severe atmospheric contamination problem. Metal organic frameworks (MOFs) and graphene are promising candidates to collect VOCs. In this study, composites which consist of graphene sheets and Cu-BTC (benzene-1,3,5 tricarboxylic acid) are prepared by the hydrothermal method to adsorb VOCs and CO. Moreover, the morphology of the resulting graphene material in the composites can be controlled by adjusting the pH value, reaction time and surfactant during the hydrothermal process, which further determines the adsorption ability for different gas molecules. According to the pore distribution features of various composites, the morphology of graphene exerts a fatal influence on the observed adsorption performances. Furthermore, the polarity of the as-prepared composites is another important determinant to selective adsorption for various VOCs. The stability of these composites under high temperature is also tested, and the results demonstrate that the adsorbents can be used in a wide temperature range. Moreover, the large BET areas and high stability of the composites in the water endow them a potential application in the sewage clarification field. After the corresponding optimization, the adsorption amounts of methanol and ethanol reach 13.6[Formula: see text]mmol[Formula: see text]g[Formula: see text] and 9.68[Formula: see text]mmol[Formula: see text]g[Formula: see text], respectively.

Electrocatalytic, Kinetic, and Mechanism Insights into the Oxygen-Reduction Catalyzed Based on the Biomass-Derived FeOx @N-Doped Porous Carbon Composites.

A valid strategy for amplifying the oxygen reduction reaction (ORR) efficiency of non-noble electrocatalyst in both alkaline and acid electrolytes by decorated with a layer of biomass derivative nitrogen-doped carbon (NPC) is proposed. Herein, a top-down strategy for the generally fabricating NPC matrix decorated with trace of metal oxides nanoparticles (FeOx NPs) by a dual-template assisted high-temperature pyrolysis process is reported. A high-activity FeOx /FeNC (namely Hemin/NPC-900) ORR electrocatalyst is prepared via simply carbonizing the admixture of Mg5 (OH)2 (CO3 )4 and NaCl as dual-templates, melamine and acorn shells as nitrogen and carbon source, hemin as a natural iron and nitrogen source, respectively. Owing to its unique 3D porous construction, large BET areas (819.1 m2 ∙g-1 ), and evenly dispersed active sites (FeNx , CN, and FeO parts), the optimized Hemin/NPC-900 catalyst displays comparable ORR catalytic activities, remarkable survivability to methanol, and preferable long-term stability in both alkali and acid electrolyte compared with benchmark Pt/C. More importantly, density function theory computations certify that the interaction between Fe3 O4 nanoparticles and arm-GN (graphitic N at armchair edge) active sites can effectually promote ORR electrocatalytic performance by a lower overpotential of 0.81eV. Accordingly, the research provides some insight into design of low-cost non-precious metal ORR catalysts in theory and practice.

ZIF-8 and three-dimensional graphene network assisted DSSCs with high performances

Dye sensitization solar cells (DSSCs) have attracted more and more attention because of the increasing energy demand and their environmental-friendly property. ZIF-8 and three-dimensional graphene network (3DGN) are adopted to modify photoanode to improve the resulting photovoltaic performances. The dye loading amount enhances significantly after adding ZIF-8 because of its large BET area and proper aperture, while the presence of 3DGN booms the fast electron transport ability based on its continuous 3D structure and high conductivity. The adsorption amount of dye molecules reaches 2.26 ​× ​10−7molcm−2, which is 2.6 times higher than that of pure TiO2 photoanode. On the other hand, the improved full factor, decreased dark current and electron impedance spectrum further confirm the function of 3DGN. After optimizing the mass fractions of ZIF-8 and 3DNG, the energy conversion efficiency reaches 8.77%, indicating the synergy between the ingredients and the feasibility of the as-prepared composite photoanode.

Cu-BTC-Assisted DSSCs with Improved Photovoltaic Performances

MOF-based composite material is adopted to modify photoanode, and the obtained large BET area is found meaningful to the dye loading amount, which brings about a high short circuit current and incident photon to current conversion efficiency. Meanwhile, three-dimensional graphene networks (3DGNs) are employed to provide a fast transport channel for photo-induced electrons. The morphology is analyzed by SEM, TEM, XRD and Raman spectrum, and the photovoltaic performances are recorded to reveal the specific functions of MOF and 3DGNs. The synergy between MOF, 3DGNs and TiO2is achieved by adjusting their mass fraction. Moreover, the average size of MOF exerts a significant influence on the resulting properties resulting from the scattering ability to incident light. After corresponding optimizing, the short circuit current, open circuit voltaic, fill factor and energy conversion efficiency reach 20.5[Formula: see text]mAcm[Formula: see text], 680[Formula: see text]mV, 0.619% and 8.63%.

High Performance Composite Photocatalysts based on Metal Organic Framework as the Modifier

Photocatalysis attracts increasing attention because of the deteriorating environment pollution. Metal organic frameworks (MOFs) is deemed as one kind of promising modifiers to improve the photocatalytic performance of traditional semiconductors by their large BET areas. In this study, reduced graphene oxide (RGO) and Cu‐BTC are utilized to decorate TiO2 to enhance the corresponding photoactivity. Morphology of the as‐prepared composite is detected by SEM and XRD curve, while the UV‐ and visible‐light activities are estimated by the decomposition of various dyes. The specific functions of Cu‐BTC and RGO are revealed by analysing the adsorption capacity, lifetime of the photoinduced electrons and the EPR profiles. The resulting Cu‐BTC‐RGO/TiO2 samples display outstanding photocatalytic properties, which are much better than that of the pure TiO2 and RGO/TiO2 samples because of the synergy between these components. Lastly, the recycle using stability and the influence from the preparation process of the composite photocatalysts are discussed.

Graphene and MOFs co-modified composites for high adsorption capacity and photocatalytic performance to remove pollutant under both UV- and visible-light irradiation

Various metal organic frameworks (MOFs) including ZIF-8, Uio-66 and Cu-BTC are prepared and adopted with reduced graphene oxide (RGO) to co-modify TiO2. The resulting composite photocatalysts display high photocatalytic performances under both UV- and visible-light irradiation, and the corresponding photocatalytic mechanisms are revealed by considering the electronic structures and morphologies of these ingredients, which are proven by IR curves, STM patterns, lifetime of photoinduced electrons. The influences of BET areas and pore diameters of the adopted MOFs on the resulting photocatalytic properties are studied, and the specific influence of interaction between TiO2 and RGO on the observed photocatalytic activities are also discussed. The large BET areas of the MOFs endow high adsorption capacities to the resulting photocatalysts, while the closely chemical contact between TiO2 and RGO achieves the visible-light activity. After optimization, the degradation rate constants of rhodamine-B reach 1.65 ​× ​10-1 min-1 and 1.12 ​× ​10-1 min-1 under UV- and visible-light irradiation, respectively.

Adsorption of low-concentration arsenic from water by co-modified bentonite with manganese oxides and poly(dimethyldiallylammonium chloride)

Inorgano–organo–bentonite (PMBt) was synthesized through co-modification of bentonite with manganese oxides and poly(dimethyldiallylammonium chloride) (PDMDAAC), and was utilized to remove low-concentration arsenic from water. The hybrid material was characterized by means of X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and N2 adsorption–desorption. It was revealed that the hybrid material possessed an amorphous structure and displayed uneven manganese oxides particles gathering about the bentonite aggregates with a large BET area of 128.90m2/g. The effects of adsorption parameters were investigated, such as stirring time, arsenic concentrations, adsorbent dose, temperature, pH, added anions and ionic strength. The adsorption kinetics and equilibrium of arsenic on the co-modified bentonite were further determined. The results revealed that the adsorption of arsenic was dramatically affected with change in solution pH and significantly suppressed by phosphate anion. The adsorption kinetic data was best fitted with the linear pseudo–second–order model and was well with the non-linear Bangham model. The equilibrium data were well simulated with the Brunauer–Emmett–Teller, Freundlich and Redlich–Peterson isotherms by either non-linear or linear regression, respectively. The non-linear Langmuir isotherm showed best fitting and the maximal adsorption capacity was 9.14–9.99mg/g, dependent on the error function used. It was suggested that the hybrid material had a heterogeneous surface and high affinity towards arsenic, which is highly favorable for arsenic adsorption following a non-ideal monolayer adsorption model. Based on the above comprehensive analysis, the plausible mechanism for arsenic adsorption on PMBt was suggested as a mixed removal mechanism i.e., electrostatic attraction followed by inner-sphere complexation.

Three-dimensional graphene monolith-based composite: superiority in properties and applications

ABSTRACTWith the development of graphene research, the three-dimensional graphene monolith (3DGM), which can be prepared by the chemical vapour deposition method (CVD-3DGM) and the self-assembly of reduced graphene oxide nanosheets (RGO-3DGM), has drawn increasing attention because of its properties and application prospects that are better than those of two-dimensional graphene nanosheets. By utilising its excellent electrical property, large BET area and favourable mechanical strength, some research findings on the 3DGM-assisted thermal interface materials, conductive polymers and films, dye-sensitised solar cells and supercapacitors have been reported. In this perspective, we review recent progress in the synthesis and application of 3DGM-based composites and devices. In particular, the advantages of the CVD-3DGM are highlighted after comparing the reports, and the specific reasons are analysed and discussed. Finally, the probable directions of development, research focus and corresponding challenges for the preparation and application of the CVD-3DGM in the future are proposed.

Morphology-controlled synthesis of Ni-B nanoparticles by addition of hydrogen peroxide

In this paper, H2O2 was used to control the morphology of Ni-B nanoparticles prepared by chemical reduction of nickel ethylenediamine complex. With increasing H2O2 concentration, Ni-B nanoparticle morphology progressed from pompon-like to sea urchin-like and finally to a flower-like shape. The controlled morphology was the result of dynamic equilibrium between the reduction of nickel ions by KBH4 and oxidation dissolution of Ni-B nanoparticles due to etching by H2O2. Additionally, the Ni-B catalyst nanoparticles had large BET areas and more uniform Ni active centers on the surface. However, excess H2O2 could disrupt the dynamic equilibrium, allowing the production of various structures of Ni-B nanoparticles. The catalyst composition with a molar ratio of 1:1 Ni ion to H2O2 showed the best activity toward electrocatalytic oxidation of ethanol.

Enhanced catalytic activity for fructose conversion on nanostructured niobium oxide after hydrothermal treatment: Effect of morphology and porous structure

This paper reports the synthesis of a new class of catalysts based on niobium using Filter Cake (FC) as precursor, which is more affordable economically than other niobium sources commonly used. FC is obtained before the necessary purification to obtain niobic acid (Nb2O5∙nH2O), making the catalyst synthesis process less costly. Its modification by hydrothermal treatment in the presence of different agents (oxalic acid or hydrogen peroxide) allowed the obtention of nanostructured materials in the form of rods or spheres with larger BET area, crystallinity and acidity than the precursor. Their catalytic potential were evaluated in fructose dehydration reaction in aqueous media, aiming the obtention of 5-hydroxymethylfurfural (5-HMF). The production of furan compounds from sugars has become a process of great interest in recent years because it is related to the search for more sustainable sources of energy, since carbohydrates are the predominant part of biomass. In optimum conditions, it was possible to obtain 22% yield of 5-HMF in aqueous medium and 47% yield of 5-HMF using DMSO as solvent.

High-performance photoanode for dye sensitized solar cells with graphene modified two-layer construction

Graphene modified dye sensitized solar cells (DSSCs) show high photovoltaic performances due to the fast electron transport capacity and the large BET area of the additive. However, the corresponding research on how to further improve the properties of DSSCs by optimizing the adopted graphene is insufficient. In this study, reduced graphene oxide (RGO) nanosheets and three-dimensional graphene networks (3DG) are employed to build high performance photoanodes with a two-layer structure by taking full advantages of them, simultaneously. Residual functional groups of RGO support preconditions to construct an electron transport layer between conducting substrate and work layer of photoanode, which is beneficial to depress dark current on the interface. On the other hand, high integrity and continuity of 3DG provide a fast electrons transport network in the work layer, which suppresses the recombination of electron–hole pairs in the photoanode. After optimizing the structure of photoanode, the energy conversion efficiency reaches 8.87%.

Synthesis of acidified palygorskite/BiOI with exceptional performances of adsorption and visible-light photoactivity for efficient treatment of aniline wastewater

The acidified palygorskite/BiOI composites with different amounts of acidified palygorskite were synthesized using an ethylene glycol-assisted solvothermal method. The morphology, structure, surface area and pore-size distribution of the composites were characterized using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and N2 adsorption–desorption isotherms. The BiOI microspheres consisting of numerous nanosheets were uniformly dispersed on the surface of acidified palygorskite. The composite with doping amount of 50wt.% acidified palygorskite manifested a large BET area of 118.5m2/g with mesoporous structure of 10.8nm. The surface chemistry was obtained by the determination of the point of zero charge. The introduction of acidified palygorskite made the composites have more acidic character. The adsorption of aniline onto acidified palygorskite/BiOI followed the pseudo-second-order model and the Freundlich equation. As pH increased, equilibrium adsorption concentration showed an upward trend, and reached a maximum at pH=7. The 50wt.%-acidified palygorskite/BiOI exhibited the optimal adsorption performance and visible-light photoactivity for 50mgL−1 of aniline solution. About 90wt.% of aniline was removed through combination of high adsorption and efficient photodegradation processes.

Synthesis and physicochemical properties of graphene/ZrO2 composite aerogels

Graphene/ZrO2 composite aerogels with large BET areas have been synthesized using a sol–gel method together with a supercritical fluid drying process.

An efficient electron storage photovoltaic cell based on TiO2/carbon aerogel composite prepared by in-situ method

An encouraging electron storage photovoltaic cell (ESPC) based on TiO2/carbon aerogel (TCA) composite prepared by in-situ method has been developed to simultaneously achieve solar energy conversion and electron storage. The structures, morphologies, and electrochemical performances of the TCAs are investigated by X-ray diffractometry, scanning and transmission electron microscopy, UV-vis absorption, charge-discharge test and electrochemical impedance spectroscopy. The uniformly dispersed TCA at 550°C shows typical porous spherical structure with the large BET area of 556.1 m2g−1. The ESPC exhibits excellent electrochemical properties with the highest open-circuit photovoltage of 750mV, the maximum short-circuit current density of 15.3mAcm−2 and the capacity retention rate of 88% after 50 cycles. And the ESPC formed by two electrodes provides a successful solution of energy conversion and electron storage simultaneously for the direct photovoltaic cells.