Zhibin Wu

Adsorptive removal of methylene blue by rhamnolipid-functionalized graphene oxide from wastewater.

In this article, a rhamnolipid-functionalized graphene oxide (RL-GO) hybrid was prepared by one-step ultrasonication and adsorptive removal of methylene blue (MB) from both artificial and real wastewater by the RL-GO was investigated. The Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), Fourier transform infrared spectrum (FT-IR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Brunauer-Emmett-Teller (BET) area and Zeta potential analysis were used to characterize the adsorbent. The results showed that RL-GO had abundant functional groups and a mesopores feature. MB adsorption by the RL-GO increased with increase in adsorbent dose, pH, temperature and initial MB concentration, while it was insensitive to ionic strength variation. The adsorption kinetics fitted well to the pseudo-second-order model with correlation coefficients greater than 0.999. The Intra-particle diffusion and Boyds film-diffusion models showed that the rate-controlled step was dominated by film-diffusion in the beginning and then followed by intra-particle diffusion. The adsorption isotherm was fitted by adsorption models with the suitability in order of BET > Freundlich > Langmuir > Temkin, based on comparison between correlation coefficients. Thermodynamic analysis of equilibriums suggested that the adsorption MB on RL-GO was spontaneous and endothermic. The adsorption mechanism was also proposed to be electrostatic attraction, π-π interaction and hydrogen bond. In addition, the real wastewater experiment, the regeneration study and the comparative cost analysis showed that the RL-GO composites could be a cost-effective and promising sorbent for MB wastewater treatment owing to its high efficiency and excellent reusability.

Facile synthesis of amino-functionalized titanium metal-organic frameworks and their superior visible-light photocatalytic activity for Cr(VI) reduction.

Porous metal-organic frameworks (MOFs) have been arousing a great interest in exploring the application of MOFs as photocatalyst in environment remediation. In this work, two different MOFs, Ti-benzenedicarboxylate (MIL-125(Ti)) and amino-functionalized Ti-benzenedicarboxylate (NH2-MIL-125(Ti)) were successfully synthesized via a facile solvothermal method. The MIL-125(Ti) and NH2-MIL-125(Ti) were well characterized by XRD, SEM, XPS, N2 adsorption-desorption measurements, thermogravimetric analysis and UV-vis diffuse reflectance spectra (DRS). It is revealed that the NH2-MIL-125(Ti) has well crystalline lattice, large surface area and mesoporous structure, chemical and thermal stability, and enhanced visible-light absorption up to 520 nm, which was associated with the chromophore (amino group) in the organic linker. Compared with MIL-125(Ti), NH2-MIL-125(Ti) exhibited more efficient photocatalytic activity for Cr(VI) reduction from aqueous solution under visible-light irradiation. The addition of hole scavenger, the hole scavenger concentration and the pH value of the reaction solution played important roles in the photo-catalytic reduction of Cr(VI). The presence of Ti(3+)-Ti(4+) intervalence electron transfer was the main reason for photo-excited electrons transportation from titanium-oxo clusters to Cr(VI), facilitating the Cr(VI) reduction under the acid condition. It was demonstrated that amino-functionalized Ti(IV)-based MOFs could be promising visible-light photocatalysts for the treatment of Cr(VI)-contained wastewater.

Photocatalytic Decontamination of Wastewater Containing Organic Dyes by Metal-Organic Frameworks and their Derivatives

Photoactive metal–organic frameworks (MOFs) have lately emerged as a class of crystalline porous materials, which provides an advanced platform to develop catalysts for the photocatalytic decolorization of wastewater. Controllable integration of pure MOFs into other active materials creates fabrication protocols for new multifunctional hybrids with superior photocatalytic properties for dye degradation into individual components, and the calcination of transition‐metal MOF precursors affords a convenient and practical route for preparation of nanosized photocatalysts with novel structures and good purity. Although the application of pure MOFs for organic pollutant decomposition has been reviewed previously, there have been significant advances in diverse MOF‐based composites and their derivatives for dye degradation, which have rarely been reviewed. This review aims to fill this gap and discuss the various influencing factors, the reaction kinetics, and mechanisms of dye degradation, considering the period from 2014 to 2016. Finally, the challenges and outlooks for dye decomposition by MOF‐based materials are suggested.

Enhanced adsorptive removal of p-nitrophenol from water by aluminum metal–organic framework/reduced graphene oxide composite

In this study, the composite of aluminum metal–organic framework MIL-68(Al) and reduced graphene oxide (MA/RG) was synthesized via a one–step solvothermal method, and their performances for p–nitrophenol (PNP) adsorption from aqueous solution were systematically investigated. The introduction of reduced graphene oxide (RG) into MIL-68(Al) (MA) significantly changes the morphologies of the MA and increases the surface area. The MA/RG-15% prepared at RG-to-MA mass ratio of 15% shows a PNP uptake rate 64% and 123% higher than MIL-68(Al) and reduced graphene oxide (RG), respectively. The hydrogen bond and π – π dispersion were considered to be the major driving force for the spontaneous and endothermic adsorption process for PNP removal. The adsorption kinetics, which was controlled by film–diffusion and intra–particle diffusion, was greatly influenced by solution pH, ionic strength, temperature and initial PNP concentration. The adsorption kinetics and isotherms can be well delineated using pseudo–second–order and Langmuir equations, respectively. The presence of phenol or isomeric nitrophenols in the solution had minimal influence on PNP adsorption by reusable MA/RG composite.

Adsorption of Estrogen Contaminants by Graphene Nanomaterials under Natural Organic Matter Preloading: Comparison to Carbon Nanotube, Biochar, and Activated Carbon

Adsorption of two estrogen contaminants (17β-estradiol and 17α-ethynyl estradiol) by graphene nanomaterials was investigated and compared to those of a multi-walled carbon nanotube (MWCNT), a single-walled carbon nanotube (SWCNT), two biochars, a powdered activated carbon (PAC), and a granular activate carbon (GAC) in ultrapure water and in the competition of natural organic matter (NOM). Graphene nanomaterials showed comparable or better adsorption ability than carbon nanotubes (CNTs), biochars (BCs), and activated carbon (ACs) under NOM preloading. The competition of NOM decreased the estrogen adsorption by all adsorbents. However, the impact of NOM on the estrogen adsorption was smaller on graphenes than CNTs, BCs, and ACs. Moreover, the hydrophobicity of estrogens also affected the uptake of estrogens. These results suggested that graphene nanomaterials could be used to removal estrogen contaminants from water as an alternative adsorbent. Nevertheless, if transferred to the environment, they would also adsorb estrogen contaminants, leading to great environmental hazards.

One-step calcination method for synthesis of mesoporous g-C3N4/NiTiO3 heterostructure photocatalyst with improved visible light photoactivity

A novel g-C3N4/NiTiO3 composite was fabricated by one-step calcination method using dicyandiamide, tetrabutyl titanate and nickel acetate as the precursors. The samples were characterized by scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, N2 adsorption/desorption isotherms, UV-vis diffuse reflection spectroscopy and photoluminescence spectroscopy. It was indicated that the hybrids owned a large surface area, mesoporous structure and improved visible light absorption. The optimal g-C3N4 content in the g-C3N4/NiTiO3 composite was 18.4 wt%, and the corresponding visible-light removal rate for nitrobenzene was 0.0132 min−1, about 1.6 times higher than that of pure NiTiO3. The enhanced photocatalytic activity may be attributed to the large surface area, stronger absorption in the visible region and efficient electron–hole separation.

Facile synthesis of CeO2 nanoparticle sensitized CdS nanorod photocatalyst with improved visible-light photocatalytic degradation of rhodamine B

A heterostructure photocatalyst consisting of one-dimensional (1D) CdS nanorods (NRs) and cerium dioxide (CeO2) nanoparticles (NPs) was successfully synthesized via a solvothermal method. Different characterization techniques confirmed that CeO2 NPs were intimately attached on CdS NRs. The visible-light-driven photocatalytic activity was evaluated by the discoloration of rhodamine B (RhB). It was indicated that, under visible light illumination, the photocatalytic rate constant of CdS/CeO2 was nearly 3.4 times and 28 times higher than that of pure CdS and pure CeO2, respectively, owing to the high oxygen storage capacity of the CdS/CeO2 heterostructure, and the inhibition of electron–hole pair recombination benefitting from efficient electron transfer from CdS NRs to CeO2 NPs. In addition, the degradation mechanism of RhB on CdS/CeO2 was also discussed. This durable nanocomposite catalyst, with its excellent combination of CdS NRs and CeO2 NPs, is able to be a promising catalyst for RhB degradation under visible-light irradiation.

Highly efficient visible-light-induced photoactivity of Z-scheme Ag2CO3/Ag/WO3 photocatalysts for organic pollutant degradation

Novel and efficient Z-scheme Ag2CO3/Ag/WO3 with excellent visible-light-driven photocatalytic performance was fabricated using a facile deposition and photochemical reduction process. Surface, morphological, and structural properties of the resulting materials were characterized using N2 sorption–desorption and Brunauer–Emmett–Teller (BET) surface area measurements, scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and UV-vis and photoluminescence spectroscopy. The photocatalytic performances of the Ag2CO3/Ag/WO3 composites were evaluated by the degradation of rhodamine B (RhB), methyl orange (MO), ciprofloxacin (CIP), and tetracycline hydrochloride (TC) under visible light irradiation. The results demonstrate that the novel Z-scheme Ag2CO3/Ag/WO3 composites exhibit higher photocatalytic activity than pure Ag2CO3 rods and WO3 nanoparticles. The enhanced photocatalytic activity of Ag2CO3/Ag/WO3 can be ascribed to the extended absorption in the visible light region caused by a surface plasmon resonance (SPR) effect, effective separation of photogenerated charges, and the formation of a Z-scheme system. In addition, the photocatalyst exhibits high stability and reusability. This work could offer a new insight into the design and fabrication of advanced materials with Z-scheme structures for photocatalytic applications for organic pollutants removal from wastewater.

Solvothermal synthesis of graphene/BiOCl0.75Br0.25 microspheres with excellent visible-light photocatalytic activity

Three-dimensional BiOCl0.75Br0.25/graphene (BG) microspheres have been synthesized via a facile solvothermal route. The as-prepared samples were characterized by powder X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), X-ray Photoelectron Spectroscopy (XPS), UV-vis diffuse reflectance spectroscopy (UV-vis DRS) and Brunauer–Emmett–Teller (BET) area. The photocatalytic activities of the samples were evaluated by the degradation of Rhodamine B (RhB) under visible light irradiation. It was shown that the BG photocatalysts with 5.0 wt% graphene (BG5.0) exhibited the highest photocatalytic activity, which was almost up to 2.3 times than that of pure BiOCl0.75Br0.25. The enhanced photoactivity of BG5.0 was mainly attributed to the effective light absorption, the larger specific surface areas and the more efficient charge transportation and separation.

Facile preparation of an Ag/AgVO3/BiOCl composite and its enhanced photocatalytic behavior for methylene blue degradation

BiOCl and AgVO3 have aroused great interest as photocatalysts in environmental remediation. They could be combined to improve their photocatalytic activity. A novel Ag/AgVO3/BiOCl composite photocatalyst was produced via a facile ultrasound assisted hydrothermal method. The as-prepared samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-vis diffuse reflectance spectroscopy (UV-DRS), photoluminescence (PL) emission spectroscopy and Brunauer Emmett Teller (BET) specific surface area analysis. It is revealed that the Ag/AgVO3/BiOCl composite was successfully synthesized with a large specific surface area, mesoporous structure, enhanced light absorption performance and good recyclability. The photocatalytic activity for methylene blue (MB) degradation was investigated under visible light irradiation. The Ag/AgVO3/BiOCl composite photocatalyst exhibited superior photocatalytic activity, and about 93.16% of MB was removed within 60 minutes of irradiation, which was better than that of pure BiOCl (29.24%) and Ag/AgVO3 (37.52%). The enhanced photocatalytic activity could be attributed to the effective visible light absorption and separation of electrons and holes. Therefore, it is reasonable to believe that the Ag/AgVO3/BiOCl composite photocatalyst has great potential in environmental remediation.