Graphene with atomic layer of sp2-hybridized carbon atoms in a hexagonal structure has attracted multidisciplinary attention since its discovery. Due to the inherent advantages of large specific ...surface area and abundant functional groups, its derivative graphene oxide (GO) nanomaterials have achieved large-scale development in effective pollution treatment. In the past few years, novel GO-based nanomaterials through coupling with other nanomaterials have been synthesized with significant process and applied for efficient elimination of different kinds of pollutants. This paper aims to summarize recent research results on the excellent removal ability of GO-based nanomaterials for various heavy metal ions in aqueous solutions. The synthesis, adsorption process characteristics and interaction mechanism of the adsorbent are emphasized and discussed. The effects of various environmental conditions are outlined. At last, a brief summary, perspective and outlook are presented. This review is intended to provide some thrilling information for the design and manufacture of GO-based nanomaterials for the elimination of heavy metal ions from wastewater in environmental pollution management.
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•Synthesis and surface modification of GO-based composites are reviewed.•Applications of different GO-based composites for metal ions elimination are reviewed.•Interaction mechanism of metal ions with GO-based composites is discussed.•Sorption capacities of metal ions on GO-based composites and other materials are compared.•Perspective of GO-based composites in pollution management is summarized.
The synthesis of graphene oxide-based materials and their application in the efficient elimination of different metal ions are summarized and compared with other materials. The interaction mechanism is discussed in detail.
Mussel-inspired polydopamine (PDA) modification of membrane is an effective alternative for improving permeation flux and anti-fouling performance. Meanwhile, efficient method for oil-water emulsions ...separation is still highly desired. However, problems, such as time-consuming process and low utilization ratio of expensive raw material, have always been stumbling block to application of this strategy. In this study, inkjet printing of dopamine (DA) followed by UV light irradiation to modify mussel-inspired polyvinylidene fluoride (PVDF) membrane was proposed. Accordingly, PVDF membrane was inkjet printed by alternately using DA inks and alkaline tris (hydroxymethyl) aminomethane (Tris) ink. The resultant membrane was then subjected to photopolymerization under UV irradiation to form a PDA layer. Successful formation of PDA layer on membrane surface was verified by series of physical and chemical methods. The optimized membrane (DA80-60/PVDF) exhibited superior oil/water separation performance with 1.5 times permeate flux higher than that of the pristine PVDF membrane and above 99% oil rejection rate. Meanwhile, the modified membranes showed satisfactory stability in aqueous solution with wide pH range (pH 2.0–7.0). The novel membrane modification method proposed in this study is facile, cost-saving and environment-friendly, serving as a competitive candidate for fabrication of efficient membranes for oil-water emulsion separation.
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•A new method integrating inkjet printing of PDA and UV irradiation was proposed.•Successful formation of PDA layer on membrane surface was verified.•The optimized membrane had superior oil-water separation performance.•The proposed membrane modification method is facile, cost-saving and environment-friendly.
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•Photodegradation of POPs by GR-based composites was comprehensively reviewed.•Recent developments in the synthesis of GR-based photocatalysts were summarized.•Catalytic mechanisms ...and roles of GR species in composites were elucidated in depth.•Challenges and future research needs in this field were insightfully suggested.
Over the last decade, two-dimensional graphene (2D GR) has brought new impetus in environmental photocatalysis, mainly benefiting from their unique physicochemical and photoelectric structural properties. Numbers of researchers have spared no effort to utilize visible-light-induced GR-based composites as catalyst platform to generate reactive species in photocatalytic oxidation technology. Herein, a comprehensive overview is presented on recent achievements of the construction and water-related applications of these photocatalysts for persistent organic pollutants (POPs) removal. A brief introduction of synthesis strategies is introduced for GR and its derivatives. Roles of GR as supports, flexible substrates and co-catalysts in composites are specifically pointed out with experimental studies. Most importantly, shortcomings (e.g., fast carrier recombination and serious photocorrosion) appeared in visible light photocatalysis and relative solutions by using GR species are clearly investigated. Based on the current research status, special attention has been paid to their promising applications on removing typical POPs, such as phenols, antibiotics, pharmaceuticals and dyes. Also, challenges (e.g., biotoxicity) and prospects are discussed for future developments in this field. This paper enriches the knowledge to deeply understand the catalytic performances and mechanisms of GR-based photocatalysts, and bring better perspectives for researchers in this field.
Soluble microbial products (SMPs) are the predominate foulants determining fouling extent in membrane bioreactors (MBRs). However, exact mechanism underlying their typical fouling behaviors remains ...unrevealed. In this study, the typical fouling behaviors of SMPs during initial operational period of a MBR were characterized. It was found that, although being low content, SMPs rather than sludge particulates preferentially adhered to membrane surface to accumulate a gel layer, and moreover, specific filtration resistance (SFR) of SMPs was approximately 700 times larger than that of the sludge particulates at operational day 3. According to energy balance principle, a unified thermodynamic mechanism underlying these fouling behaviors of SMPs was proposed. Thermodynamic analyses demonstrated that, the attractive interaction energy strength in contact between SMPs and membrane was larger by around 3700 times than that between sludge particulates and membrane, well explaining the extremely high adhesive ability of SMPs over sludge particlulates. Meanwhile, filtration through a SMPs layer was modelled and simulated as a thermodynamic process. Simulation on an agar gel showed that, about 92.6% of SFR was originated from mixing free energy change during filtration. Such a result satisfactorily interpreted the extremely high SFR of SMPs layer over sludge cake layer. The revealed thermodynamic mechanism underlying SMPs fouling behaviors significantly deepened understanding of fouling, and facilitated to development of effective fouling control strategies.
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•Soluble microbial products (SMPs) preferentially adhered to membrane surface.•Specific filtration resistance (SFR) of SMPs was about 700 times of sludge SFR.•A unified thermodynamic mechanism of SMPs' fouling behaviors was proposed.•Interaction energy strength for SMPs was about 3700 times of that for sludge particulates.•About 92.6% of SFR was originated from mixing free energy change in SMPs filtration.
Observational studies of the relationship between hyperuricemia and the incidence of hypertension are controversial. We conducted a systematic review and meta-analysis to assess the association and ...consistency between uric acid levels and the risk of hypertension development.
We searched MEDLINE, EMBASE, CBM (Chinese Biomedicine Database) through September 2013 and reference lists of retrieved studies to identify cohort studies and nested case-control studies with uric acid levels as exposure and incident hypertension as outcome variables. Two reviewers independently extracted data and assessed study quality using Newcastle-Ottawa Scale. Extracted information included study design, population, definition of hyperuricemia and hypertension, number of incident hypertension, effect sizes, and adjusted confounders. Pooled relative risks (RRs) and corresponding 95% confidence intervals (CIs) for the association between hyperuricemia and risk of hypertension were calculated using a random-effects model.
We included 25 studies with 97,824 participants assessing the association between uric acid and incident hypertension in our meta-analysis. The quality of included studies is moderate to high. Random-effects meta-analysis showed that hyperuricemia was associated with a higher risk of incident hypertension, regardless of whether the effect size was adjusted or not, whether the data were categorical or continuous as 1 SD/1 mg/dl increase in uric acid level (unadjusted: RR = 1.73, 95% CI 1.46∼2.06 for categorical data, RR = 1.22, 95% CI 1.03∼1.45 for a 1 SD increase; adjusted: RR = 1.48, 95% CI 1.33∼1.65 for categorical data, RR = 1.15, 95% CI 1.06∼1.26 for a 1 mg/dl increase), and the risk is consistent in subgroup analyses and have a dose-response relationship.
Hyperuricemia may modestly increase the risk of hypertension incidence, consistent with a dose-response relationship.
In this study, fouling propensities of loosely bound extracellular polymeric substances (LB-EPSs) and tightly bound EPSs (TB-EPSs) in a membrane bioreactor (MBR) were investigated. It was found that, ...both the LB-EPSs and TB-EPSs possessed rather high specific filtration resistance (SFR), and LB-EPSs possessed about three times higher SFR but a lower adhesion ability than the TB-EPSs. A series of characterizations demonstrated that LB-EPSs had higher ratio of proteins to polysaccharides (PN/PS ratio), lower CO bonds content, higher hydrophilicity, higher deformation or mixing ability and more abundant high molecular weight (MW) substances than TB-EPSs. Thermodynamic analyzes revealed that the total interaction energy between the TB-EPSs and membrane was always attractive and strengthened, well explaining the higher adhesion ability of the TB-EPSs than the LB-EPSs. Meanwhile, the filtration process was found to be associated with gel layer formation, and the high SFR of EPSs was caused by the chemical potential change in gel layer filtration. According to the Flory-Huggins lattice theory, LB-EPSs tended to form a gel layer with higher cross-linking and/or polymer entanglement level because they contained more abundant high molecular weight (MW) substance, corresponding to higher SFR than that of the TB-EPSs. The proposed thermodynamic mechanisms well interpreted the different fouling propensities of LB-EPSs and TB-EPSs in MBRs.
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•Both LB-EPSs and TB-EPSs possessed ultrahigh specific filtration resistance (SFR).•LB-EPSs possessed 3 times higher SFR but lower adhesion ability than TB-EPSs.•LB-EPSs had higher PN/PS ratio, hydrophilicity and molecular weight than TB-EPSs.•TB-EPSs had higher adhesion ability due to the higher total interaction with membrane.•LB-EPSs had higher SFR due to the ease to form more homogeneous gel layer.
In the last years, anaerobic membrane bioreactor (AnMBR) technology is being considered as a very appealing alternative for wastewater treatment due to the significant advantages over conventional ...anaerobic treatment and aerobic membrane bioreactor (MBR) technology. Many articles have touted the diverse potential applications of AnMBR in various stream treatment, and membrane fouling issues. In current review, the fundamentals of AnMBR (including advantages and configurations, membrane materials and modules, and history development), application development in various stream treatment, and membrane fouling researches are summarized and critically assessed. The characteristics of AnMBR and aerobic MBR for wastewater treatment are also compared. AnMBR technology appears to be suitable for treatment of various streams, especially for food industrial wastewater and municipal wastewater. AnMBR treatment usually encounters more serious membrane fouling problem. This, however, can be remedied through various conventional and novel membrane fouling control or cleaning measures. Based on the review, future research perspectives relating to its application and membrane fouling research are proposed.
► Recent progress in AnMBRs treating various wastewaters is summarized. ► Advances in membrane fouling control strategies in AnMBRs are addressed. ► Research directions regarding AnMBR technology are identified. ► AnMBR is a promising technology for wastewater treatment and reuse.
Heteroatom doping of carbon quantum dots not only enables great improvement of fluorescence efficiency and tunability of fluorescence emission, but also provides active sites in carbon dots to ...broaden their application in sensor. Silicon as a biocompatible element offers a promising direction for doping of carbon quantum dots. Si-doped carbon quantum dots (SiCQDs) were synthesized through a facile and effective approach. The as-prepared Si-doped carbon quantum dots possess visible fluorescence with high quantum yield up to 19.2%, owing to fluorescence enhancement effect of introduced silicon atoms into carbon dots. The toxicity test on human Hela cells showed that SiCQDs have lower cellular toxicity than common CQDs, and bioimaging experiments clearly demonstrated their excellent biolabelling ability and outstanding performance in resistance to photobleaching. Strong fluorescence quenching effect of Fe(III) on SiCQDs can be used for its selective detection among general metal ions. Specific electron transfer between SiCQDs and hydrogen peroxide enables SiCQDs as a sensitive fluorescence sensing platform for hydrogen peroxide. The subsequent fluorescence recovery induced by removal of hydrogen peroxide from SiCQDs due to formation of the stable adducts between hydrogen peroxide and melamine was taken advantage of to construct effective sensor for melamine.
Extracellular polymeric substances (EPSs) are key biological substances, which largely determine properties of sludge flocs, including hydrophobicity, adhesion, flocculation, settling and dewatering ...properties, and therefore significantly affect membrane fouling in membrane bioreactors (MBRs). Much progress has been achieved in understanding of EPSs and their interrelations with membrane fouling due to a large number of systematic papers published in the last three decades. In this paper, the fundamentals of EPSs including definitions, compositions and properties are summarized. The interrelations of EPSs with other foulants in MBRs are clarified. Roles of EPSs in membrane fouling mechanisms in MBRs are critically assessed. Furthermore, factors affecting EPSs production and characteristics are summarized, and based on which, EPSs control towards membrane fouling mitigation in MBRs are comprehensively discussed. Finally, future research perspectives regarding EPSs and membrane fouling are proposed.
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•Fundamentals of EPSs including composition and properties are summarized.•Roles of EPSs in membrane fouling in MBRs are addressed.•Factors affecting EPSs in MBRs are summarized.•Strategies of EPSs control towards fouling mitigation are discussed.•Research directions regarding fouling caused by EPSs are identified.
While molecular weight distribution (MWD) is one of the most important properties of soluble microbial products (SMPs), mechanisms underlying effects of MWD of SMPs on membrane fouling have not well ...unveiled. In this study, it was found that, the supernatant of sludge suspension in a membrane bioreactor (MBR) for wastewater treatment can be fractionated into a series of SMPs samples with different molecular weight (MW) fraction. The real gel sample mainly formed by the rejected SMPs on membrane surface had a high specific filtration resistance (SFR) of 1.21 × 1016 m−1 kg−1. The SFR of SMPs samples and the model foulants of polyethylene glycol (PEG) increased with their MW. The change trend of SFR with MW cannot be sufficiently explained by three-dimensional excitation-emission matrix (EMM) and chemical compositions. Tyndall effect analysis indicated that gelating ability of SMPs and PEG in the solution increased with their MW. Scanning electron microscope (SEM) confirmed gel structure changes with the PEG MW. Accordingly, mechanisms based on Carman–Kozeny equation and Flory–Huggins lattice theory were proposed to interpret SFR of SMPs with low and high MW, respectively. Simulating these two mechanistic models on PEG samples resulted in the comparable SFR data to the experimental ones, indicating the correctness and feasibility of the proposed mechanisms. The proposed mechanisms provided in-depth understanding of membrane fouling regarding MW, facilitating to develop effective membrane fouling mitigation strategies.
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•Specific filtration resistance (SFR) of SMPs increased with molecular weight (MW).•Gelating ability of SMPs and PEG in the solution increased with their MW.•Carman–Kozeny equation based mechanism governed SFR of SMPs with low MW.•Flory–Huggins lattice theory well explained SFR of SMPs with high MW.
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