► Metal-organic frameworks are very effective to remove hazardous materials. ► Mechanisms for adsorptive removal with MOFs were summarized. ► MOFs are surely regarded as potential adsorbents for clean environment. Efficient removal of hazardous materials from the environment has become an important issue from a biological and environmental standpoint. Adsorptive removal of toxic components from fuel, waste-water or air is one of the most attractive approaches for cleaning technologies. Recently, porous metal-organic framework (MOF) materials have been very promising in the adsorption/separation of various liquids and gases due to their unique characteristics. This review summarizes the recent literatures on the adsorptive removal of various hazardous compounds mainly from fuel, water, and air by virgin or modified MOF materials. Possible interactions between the adsorbates and active adsorption sites of the MOFs will be also discussed to understand the adsorption mechanism. Most of the observed results can be explained with the following mechanisms: (1) adsorption onto a coordinatively unsaturated site, (2) adsorption via acid-base interaction, (3) adsorption via π-complex formation, (4) adsorption via hydrogen bonding, (5) adsorption via electrostatic interaction, and (6) adsorption based on the breathing properties of some MOFs and so on.
Pharmaceuticals and personal care products (PPCPs) have been detected as contaminants of emerging concern ubiquitously in the aquatic environment in China and worldwide. A clear picture of PPCP contamination in the Chinese aquatic environment is needed to gain insight for both research and regulatory needs (e.g. monitoring, control and management). The occurrence data of 112 PPCPs in waters and sediments in China has been reviewed. In most cases, the detected concentration of these PPCPs in waters and sediments were at ng/L and ng/g levels, which were lower than or comparable to those reported worldwide. A screening level risk assessment (SLERA) identified six priority PPCPs in surface waters, namely erythromycin, roxithromycin, diclofenac, ibuprofen, salicylic acid and sulfamethoxazole. The results of SLERA also revealed that the hot spots for PPCP pollution were those river waters affected by the megacities with high density of population, such as Beijing, Tianjin, Guangzhou and Shanghai. Limitations of current researches and implications for future research in China were discussed. Some regulatory issues were also addressed.
Oily sludge is one of the most significant solid wastes generated in the petroleum industry. It is a complex emulsion of various petroleum hydrocarbons (PHCs), water, heavy metals, and solid particles. Due to its hazardous nature and increased generation quantities around the world, the effective treatment of oily sludge has attracted widespread attention. In this review, the origin, characteristics, and environmental impacts of oily sludge were introduced. Many methods have been investigated for dealing with PHCs in oily sludge either through oil recovery or sludge disposal, but little attention has been paid to handle its various heavy metals. These methods were discussed by dividing them into oil recovery and sludge disposal approaches. It was recognized that no single specific process can be considered as a panacea since each method is associated with different advantages and limitations. Future efforts should focus on the improvement of current technologies and the combination of oil recovery with sludge disposal in order to comply with both resource reuse recommendations and environmental regulations. The comprehensive examination of oily sludge treatment methods will help researchers and practitioners to have a good understanding of both recent developments and future research directions.
► The review focuses on the Cr speciation, uses, toxicity and remediation aspects. ► Assessed amount of hexavalent Cr in soils/metallurgical/other wastes and sites. ► Chemical and bioremediation processes for Cr(VI) are summarised in detail. ► Strategy for bio-remediation of Cr(VI) in different solid wastes is suggested. ► Capability of microbes for reducing Cr(VI) contamination described. ► Mechanism of microbial reduction of Cr(VI) to Cr(III) is included. Chromium is a highly toxic non-essential metal for microorganisms and plants, and its occurrence is rare in nature. Lower to higher chromium containing effluents and solid wastes released by activities such as mining, metal plating, wood preservation, ink manufacture, dyes, pigments, glass and ceramics, tanning and textile industries, and corrosion inhibitors in cooling water, induce pollution and may cause major health hazards. Besides, natural processes (weathering and biochemical) also contribute to the mobility of chromium which enters in to the soil affecting the plant growth and metabolic functions of the living species. Generally, chemical processes are used for Cr- remediation. However, with the inference derived from the diverse Cr-resistance mechanism displayed by microorganisms and the plants including biosorption, diminished accumulation, precipitation, reduction of Cr(VI) to Cr(III), and chromate efflux, bioremediation is emerging as a potential tool to address the problem of Cr(VI) pollution. This review focuses on the chemistry of chromium, its use, and toxicity and mobility in soil, while assessing its concentration in effluents/wastes which becomes the source of pollution. In order to conserve the environment and resources, the chemical/biological remediation processes for Cr(VI) and their efficiency have been summarised in some detail. The interaction of chromium with various microbial/bacterial strains isolated and their reduction capacity towards Cr(VI) are also discussed.
The aim of this study was to quantify the influence of the two main categories of factors determining the yield and properties of biochar, i.e., feedstock properties and production conditions, here represented by the highest treatment temperature (HTT). To achieve this, a wide range of production temperatures (200–650 °C) and an extensive set of diverse feedstock ( = 12) were used to calculate the sensitivity. The quantitative evaluation was based on statistical analysis of coefficients of variation, and thus derived indices representing the extent of influence of the two factors, i.e., a feedstock-depended heterogeneity ( ) and a temperature-depended heterogeneity ( ). The results showed that both feedstock properties and production conditions are important for determining the yield and properties of biochar, but their respective influence changes with the property or set of properties of interest. The biochar parameters most affected by feedstock properties were e.g., total organic carbon, fixed carbon, and mineral elements of biochar. On the other hand, biochar surface area and pH was mainly influenced by highest treatment temperature. Biochar recalcitrance was mainly determined by production temperature, while the potential total C sequestration (product of recalcitrance and pyrolysis carbon yield) depended more on feedstock. Overall, the work sheds some light on the relative importance of different biochar production process parameters on the final biochar product, which is an important step towards “designed” biochar.
Copper (Cu ) containing wastewaters are extensively released from different industries and its excessive entry into food chains results in serious health impairments, carcinogenicity and mutagenesis in various living systems. An array of technologies is in use to remediate Cu from wastewaters. Adsorption is the most attractive option due to the availability of cost effective, sustainable and eco-friendly bioadsorbents. The current review is dedicated to presenting state of the art knowledge on various bioadsorbents and physico-chemical conditions used to remediate Cu from waste streams. The advantages and constraints of various adsorbents were also discussed. The literature revealed the maximum Cu adsorption capacities of various bioadsorbents in the order of algae > agricultural and forest > fungal > bacterial > activated carbon > yeast. However, based on the average Cu adsorption capacity, the arrangement can be: activated carbon > algal > bacterial > agriculture and forest-derived > fungal > yeast biomass. The data of Cu removal using these bioadsorbents were found best fit both Freundlich and Langmuir models. Agriculture and forest derived bioadsorbents have greater potential for Cu removal because of higher uptake, cheaper nature, bulk availability and mono to multilayer adsorption behavior. Higher costs at the biomass transformation stage and decreasing efficiency with desorption cycles are the major constraints to implement this technology.
Adsorption and ion exchange can be effectively employed for the treatment of metal-contaminated wastewater streams. The use of low-cost materials as sorbents increases the competitive advantage of the process. Natural and modified minerals have been extensively employed for the removal of nickel and zinc from water and wastewater. This work critically reviews existing knowledge and research on the uptake of nickel and zinc by natural and modified zeolite, bentonite and vermiculite. It focuses on the examination of different parameters affecting the process, system kinetics and equilibrium conditions. The process parameters under investigation are the initial metal concentration, ionic strength, solution pH, adsorbent type, grain size and concentration, temperature, agitation speed, presence of competing ions in the solution and type of adsorbate. The system's performance is evaluated with respect to the overall metal removal and the adsorption capacity. Furthermore, research works comparing the process kinetics with existing reaction kinetic and diffusion models are reviewed as well as works examining the performance of isotherm models against the experimental equilibrium data.
► Synthesis of ultra-small ZnS and ZnS:Fe QDs in aqueous media. ► Characterization of QDs by TEM, XRD, FAAS and UV–vis absorption techniques. ► The new report on the photocatalytic behavior of QDs on removal of MG. ► Effective degrade of dye by novel modified QDs up to 98%. The heterogeneous photocatalysis using UV-radiation and quantum dots (QDs) is an interesting method for the treatment of water polluted with the organic substances. In this study, ZnS QDs, as a pure and doped with Fe , were prepared for photodecolorization of malachite green (MG) as a model dye. The synthesis of QDs was carried out using a chemical precipitation method in aqueous solution, in the presence of 2-mercaptoethanol as a capping agent. The XRD patterns indicated that the doped nanoparticles are crystalline, with cubic zinc blend structure. The effects of dopant content, pH, nanophotocatalyst amount, irradiation time, and initial dye concentration on the removal efficiency of MG were studied. Results showed that the QDs presented high MG decolorization efficiency, and doping with Fe promoted the dye removal. The maximum removal of dyes was obtained at 80 mg/L of photocatalyst as an optimum value for the dosage of photocatalyst in pH of 8.0.
MCM-41-supported nanoscale zero-valent iron (nZVI) was sytnhesized by impregnating the mesoporous silica martix with ferric chloride, followed by chemical reduction with NaHB . The samples were studied with a combination of characterization techniques such as powder X-ray diffraction (XRD), Fourier-transform infrared (FT-IR) and Mössbauer spectroscopy, N adsorption measurements, transmission electron microscopy (TEM), magnetization measurements, and thermal analysis methods. The experimental data revealed development of nanoscale zero-valent iron particles with an elliptical shape and a maximum size of ∼80 nm, which were randomly distributed and immobilized on the mesoporous silica surface. Surface area measurements showed that the porous MCM-41 host matrix maintains its hexagonal mesoporous order structure and exhibits a considerable high surface area (609 m /g). Mössbauer and magnetization measurements confirmed the presence of core–shell iron nanoparticles composed of a ferromagnetic metallic core and an oxide/hydroxide shell. The kinetic studies demonstrated a rapid removal of Cr(VI) ions from the aqueous solutions in the presence of these stabilized nZVI particles on MCM-41, and a considerably increased reduction capacity per unit mass of material in comparison to that of unsupported nZVI. The results also indicate a highly pH-dependent reduction efficiency of the material, whereas their kinetics was described by a pseudo-first order kinetic model.
A magnetic nanoscaled catalyst cobalt ferrite (CoFe O ) was successfully prepared and used for the activation of oxone to generate sulfate radicals for the degradation of diclofenac. The catalyst was characterized by transmission electron microscopy, X-ray diffractometry, Fourier transform infrared spectroscopy and vibrating sample magnetometer. The effects of calcination temperature, initial pH, catalyst and oxone dosage on the degradation efficiency were investigated. Results demonstrated that CoFe O -300 exhibited the best catalytic performance and almost complete removal of diclofenac was obtained in 15 min. The degradation efficiency increased with initial pH decreasing in the pH range of 5–9. The increase of catalyst and oxone dosage both had the positive effect on the degradation of diclofenac. Moreover, CoFe O could retain high degradation efficiency even after being reused for five cycles. Finally, the major diclofenac degradation intermediates were identified and the primary degradation pathways were proposed.
► Silver/iron oxide nanoparticles were synthesized via a facile one-pot green process. ► Arginine created a solution of pH 10 and acted as a reducing agent. ► Good catalytic activity and stability for 4-nitrophenol reduction were demonstrated. ► This magnetically recoverable silver nanocatalyst was useful in wastewater treatment. Silver/iron oxide composite nanoparticles have been synthesized successfully via a facile one-pot green route by the use of -arginine, which created an aqueous solution of about pH 10 and acted as a reducing agent for the successive formation of iron oxide and Ag nanoparticles. The product was characterized to be silver-coated iron oxide and iron oxide hydroxide composite nanoparticles with a mean diameter of about 13.8 ± 3.0 nm and 8.53% of Ag in weight. It exhibited good catalytic activity for the reduction of 4-nitrophenol to 4-aminophenol with sodium borohydride. The reduction reaction followed the pseudo-first-order kinetics. The corresponding rate constants increased with the increases of temperature and catalyst amount but decreased with the increase of initial 4-NP concentration, revealing an activation energy of 28.2 kJ/mol and a diffusion controlled mechanism. In addition, this product had quite good stability. No significant activity loss was observed after reuse for 5 cycles.
Photosensitization of TiO with other transition metal oxides can extend its light absorption property in the visible region. Such materials could emerge as excellent catalysts for solar photocatalytic degradation. In the present study mesoporous Fe O /TiO (10, 30, 50, 70 and 90 wt% Fe O ) photocatalysts were synthesized by sol–gel process and characterized using different techniques. The XRD patterns exhibited the presence of mesoporous structure and isomorphic substitution of Fe in TiO at low Fe loading and Ti in Fe O at high Fe loading. The XPS results revealed the presence of Ti and Fe in Fe O /TiO materials. The DRS UV–vis spectra showed a shift in the band gap excitation of TiO to longer wavelength, thus illustrating incorporation of Fe in TiO . In addition, free TiO and Fe O particles were also present. Their photocatalytic activity was tested for the degradation of 4-chlorophenol in aqueous medium using sunlight. The activity of the catalysts followed the order: meso-30 wt% Fe O /TiO > meso-10 wt% Fe O /TiO > meso-50 wt% Fe O /TiO > meso-70 Fe O /TiO > meso-90 wt% Fe O /TiO > meso-Fe O > meso-TiO . This order concluded that mesoporous Fe O /TiO could be an active catalyst for pollutant degradation, as TiO with framework Fe and photosensitization with free Fe O were involved in the activity.
► GO–CdS composites were prepared through a novel two-phase mixing method. ► Uniform deposition of CdS nanoparticles on GO sheets. ► Reduced charge recombination rate. ► Enhanced photo-stability. ► High photodegradation and disinfection efficiency. Graphene oxide (GO)–CdS composites were synthesized via a novel two-phase mixing method successfully. CdS nanoparticles were uniformly self-assembled on GO sheets at water/toluene interface. The photocatalytic degradation (photodegradation) and disinfection activities of GO–CdS composites were investigated thoroughly. The results show that GO–CdS composites exhibit higher efficiency in photodegradation of various water pollutants than pure CdS nanoparticles under visible light irradiation. In addition, the interactions between GO sheets and CdS nanoparticles inhibit the photo-corrosion of CdS and leaching of Cd . Only 3.5 wt% Cd of GO–CdS was leached out after photodegradation, while 38.6 wt% Cd of CdS was lost into aqueous solution. Furthermore, the disinfection activity of GO–CdS composites was investigated for the first time. Nearly 100% of both Gram-negative ( ) and Gram-positive ( ) were killed within 25 min under visible light irradiation. The excellent performances of GO–CdS composites can be attributed to that (1) effective charge transfer from CdS to GO reduces the recombination rate of photo-generated electron–hole pairs; (2) uniform deposition of CdS on GO sheets eliminates aggregation of CdS nanoparticles; and (3) the strong interactions between GO and CdS enhancing the durability of GO–CdS composites. Finally, the mechanism behind these excellent performances was verified by transient photocurrent measurement and further confirmed by ESR technique as well as employing a radical scavenging species – dimethyl sulfoxide (DMSO).
The influence of persulfate activation methods on polycyclic aromatic hydrocarbons (PAHs) degradation was investigated and included thermal, citrate chelated iron, and alkaline, and a hydrogen peroxide (H O )-persulfate binary mixture. Thermal activation (60 °C) resulted in the highest removal of PAHs (99.1%) and persulfate consumption during thermal activation varied (0.45–1.38 g/kg soil). Persulfate consumption (0.91–1.22 g/kg soil) and PAHs removal (73.3–82.9%) varied using citrate chelated iron. No significant differences in oxidant consumption and PAH removal was measured in the H O –persulfate binary mixture and alkaline activated treatment systems, relative to the unactivated control. Greater removal of high molecular weight PAHs was measured with persulfate activation. Electron spin resonance spectra indicated the presence of hydroxyl radicals in thermally activated systems; weak hydroxyl radical activity in the H O –persulfate system; and superoxide radicals were predominant in alkaline activated systems. Differences in oxidative ability of the activated persulfate were related to different radicals generated during activation.
Chemically activated biochar produced under oxygenated (O-biochar) and oxygen-free (N-biochar) conditions were characterized and the adsorption of endocrine disrupting compounds (EDCs): bisphenol A (BPA), atrazine (ATR), 17 α-ethinylestradiol (EE2), and pharmaceutical active compounds (PhACs); sulfamethoxazole (SMX), carbamazepine (CBM), diclofenac (DCF), ibuprofen (IBP) on both biochars and commercialized powdered activated carbon (PAC) were investigated. Characteristic analysis of adsorbents by solid-state nuclear magnetic resonance (NMR) was conducted to determine better understanding about the EDCs/PhACs adsorption. N-biochar consisted of higher polarity moieties with more alkyl (0–45 ppm), methoxyl (45–63 ppm), O-alkyl (63–108 ppm), and carboxyl carbon (165–187 ppm) content than other adsorbents, while aromaticity of O-biochar was higher than that of N-biochar. O-biochar was composed mostly of aromatic moieties, with low H/C and O/C ratios compared to the highly polarized N-biochar that contained diverse polar functional groups. The higher surface area and pore volume of N-biochar resulted in higher adsorption capacity toward EDCs/PhACs along with atomic-level molecular structural property than O-biochar and PAC. N-biochar had a highest adsorption capacity of all chemicals, suggesting that N-biochar derived from loblolly pine chip is a promising sorbent for agricultural and environmental applications. The adsorption of pH-sensitive dissociable SMX, DCF, IBP, and BPA varied and the order of adsorption capacity was correlated with the hydrophobicity (K ) of adsorbates throughout the all adsorbents, whereas adsorption of non-ionizable CBM, ATR, and EE2 in varied pH allowed adsorbents to interact with hydrophobic property of adsorbates steadily throughout the study.
Novel visible-light-driven graphitic carbon nitride (g-C N )/WO composite photocatalysts were prepared, and the acetaldehyde (CH CHO) degradation activity of these composites was evaluated. The prepared g-C N /WO composites were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), ultraviolet–visible diffuse reflection spectroscopy (UV–vis), and the N gas adsorption Brunauer–Emmett–Teller (BET) method (N -BET). The WO particles, which were 100–300 nm in size, were in direct contact with the g-C N sheet surface. The optical band gap and specific surface area of the g-C N /WO composites were in the range of 2.65–2.75 eV and 4–7 m /g, respectively. The g-C N /WO composites exhibited higher activity for the photodegradation of CH CHO under visible light irradiation compared to g-C N . The optimal WO content for the CH CHO photodegradation activity of the heterojunction structures was determined. The synergistic effect of g-C N and WO was considered to lead to improved photogenerated carrier separation. A possible degradation mechanism of CH CHO over the g-C N /WO composite photocatalyst under visible light irradiation was proposed. These results should usefully expand applications of g-C N as a visible-light-driven photocatalyst.
► Ag PO /GO shows enhanced photocatalytic activity in degradation of dyes in water. ► The sample with GO content of 15% exhibits the best activity under visible light. ► The combination of GO enhances the separation efficiency of photo-induced carriers. Ag PO /graphene-oxide (Ag PO /GO) composite has been synthesized by a liquid phase deposition method, and used for the photodegradation of organic dyes in water under visible light. The as-synthesized samples were characterized by X-ray diffraction, scanning electron microscope, N sorption–desorption, and UV–vis diffuse reflectance spectra. The SEM image indicated that Ag PO particles were mainly distributed on the surface of GO sheets uniformly. DRS analysis revealed that the samples had good visible light response. The photocatalytic activity of Ag PO /GO composite was evaluated by decomposing of dyes (such as methyl orange, rhodamine B) in water under visible or UV–vis light irradiation. The degradation results indicated that the photocatalytic performance of Ag PO /GO was greatly enhanced due to the improved adsorption performance and separation efficiency of photo-generated carriers. The Ag PO /GO composite with GO content of 15 wt.% exhibited superior activity under visible light irradiation. After 50 min of reaction, the degradation ratio of MO was about 86.7%, while RhB solution could be completely degraded within 30 min of reaction. Further study proved that the direct oxidation of pollutants by holes has played a major role in the degradation process. The results of this work would provide a new sight for the construction of visible light-responsive photocatalysts with high performance.
Degradation of antipyrine (AP) in water by three UV-based photolysis processes (i.e., direct UV, UV/H O , UV/persulfate (UV/PS)) was studied. For all the oxidation processes, the AP decomposition exhibited a pseudo-first-order kinetics pattern. Generally, UV/H O and UV/PS significantly improved the degradation rate relevant to UV treatment alone. The pseudo-first-order degradation rate constants ( ) were, to different degrees, affected by initial AP concentration, oxidant dose, pH, UV irradiation intensity, and co-existing chemicals such as humic acid, chloride, bicarbonate, carbonate and nitrate. The three oxidation processes followed the order in terms of treatment costs: UV/PS > UV > UV/H O if the energy and chemical costs are considered. Finally, the AP degradation pathways in the UV/H O and UV/PS processes are proposed. Results demonstrated that UV/H O and UV/PS are potential alternatives to control water pollution caused by emerging contaminants such as AP.
A series of the amphoteric grafting flocculants, carboxymethyl chitosan-graft-polyacrylamide, has been prepared and employed for removal of both anionic and cationic dyes from aqueous solutions. In the current work, a series of amphoteric grafting chitosan-based flocculants (carboxymethyl chitosan- -polyacrylamide, denoted as CMC- -PAM) was designed and prepared successfully. The flocculants were applied to eliminate various dyes from aqueous solutions. Among different graft copolymers, CMC- -PAM11 with a PAM grafting ratio of 74% demonstrated the most efficient performance for removal of both the anionic dye (Methyl Orange, MO) and the cationic dye (Basic Bright Yellow, 7GL) under the corresponding favored conditions (80 mg/L of the flocculant at pH 4.0, and 160 mg/L at pH 11.0). In comparison with its precursors, chitosan and carboxymethyl chitosan, CMC- -PAM11 showed higher removal efficiencies and wider flocculation windows. More importantly, the graft copolymer produced notably more compacted flocs based on image analysis in combination with fractal theory, which was of great significance in practical water treatment. Furthermore, the flocculation mechanism was discussed in detail. The grafted polyacrylamide chains were found to contribute much to the improved bridging and sweeping flocculation effects, but reduced charge neutralization flocculation for the effect of charge screening.