Treatment Of Heavy Metal-contaminated Water Research Articles

Role of algae-bacterial consortium in heavy metal contaminated water treatment

Role of algae-bacterial consortium in heavy metal contaminated water treatment

Role Of Algae-Bacterial Consortium In Heavy Metal Contaminated Water Treatment

Heavy metal pollution of the environment is a global issue that has an impact on all types of natural life. Arsenic (As) and Cadmium (Cd), along with other heavy metals, permeate our environment and have a number of negative impacts. As and Cd are harmful compounds that are currently prevalent everywhere as a result of water pollution, temperature rise, and climate change in aquatic ecosystems. Using bacteria and algae to remove, decompose, or render harmless contaminants and harmful chemicals (As and Cd) in aquatic systems is currently gaining more attention. the use of bioremediation to remove heavy metals from aquatic environments. Heavy metal pollution of the environment is a global issue that has an impact on all types of natural life. Arsenic (As) and Cadmium (Cd), along with other heavy metals, permeate our environment and have a number of negative impacts. As and Cd are harmful compounds that are currently prevalent everywhere as a result of water pollution, temperature rise, and climate change in aquatic ecosystems. Using bacteria and algae to remove, decompose, or render harmless contaminants and harmful chemicals (As and Cd) in aquatic systems is currently gaining more attention. the use of bioremediation to remove heavy metals from aquatic environments.

Coffee grounds modified zero-valent iron for efficient heavy metal removal

Surface modification is one of the most important approach for improving the reactivity of zero-valent iron. In this study, waste coffee grounds (CG) were chosen to modify zero-valent iron through a mechanochemical method. The synthesized CG-ZVI exhibited a 166 times faster Cr(VI) removal rate. Structural characterization and ATR-FTIR analysis indicated that CG modification endowed ZVI with abundant carboxylic acid groups, and accelerated the adsorption of Cr(VI) via the complexation effect of CG-COOH···HCrO4−. Moreover, the polyphenolic substances from CG-ZVI, as an electron shuttle, accelerated the electron transfer from the iron core to generated surfaced bound Fe2+, resulting in high efficiency of Cr(VI) removal. In addition, CG-ZVI selectively removed Cr(VI) in the presence of anions (Cl−, NO3−, SO42−) and acted as a permeable reactive barrier material for in situ treatment of heavy metal-contaminated water. This work demonstrates that CG modification can function as an excellent candidate for perfecting the reactivity of ZVI. More importantly, it opens up a new way for the utilization of discarded CG.

Application of CO2-loaded geopolymer in Zn removal from water: A multi-win strategy for coal fly ash disposal, CO2 emission reduction, and heavy metal-contaminated water treatment

Coal fly ash accumulation, global warming, and heavy metal-contaminated water environments are three primary environmental concerns. Porous geopolymers are economical porous adsorbents that can be produced using coal fly ash as a raw material and employed for heavy metal removal from water. However, residual alkalis on the geopolymer can lead to extreme increases in pH and cause environmental stresses, which limits the large-scale production and application of geopolymers in industries and environments. A green approach to alleviating the high basicity of geopolymers through CO2 exposure is proposed, with CO2 adsorption experiments as well as Zn removal batch and column experiments conducted to evaluate the practicality of the synergistic strategy. CO2 adsorption experiments show the CO2 capture capacity of fresh geopolymer (F@PG) is 0.80 mmol g−1, greater than that of the conventionally washed geopolymer (W@PG, 0.26 mmol g−1), with the pH of the geopolymer decreasing after both washing and CO2 exposure. Batch experiments suggest neither washing nor CO2 exposure cause a significant change in the Zn adsorption capacity of the geopolymer; column experiments show the CO2-exposed geopolymer (C@PG) has a pH < 9.5 and a satisfactory Zn removal performance similar to W@PG, but F@PG with a pH ∼12 results in a conversion of Zn to anionic forms and a decrease in Zn removal efficiency. These results indicate CO2 exposure is a practical method to decrease the pH of geopolymers for applications related to heavy metal-contaminated water treatment and provide a large-scale industrial option for coal fly ash consumption and CO2 emission reduction.

Preparation of Functionalized Palm Kernel Shell Bio-adsorbent for the treatment of heavy metal-contaminated water

Human beings and living creatures are at great risk because of heavy metal contamination in water resulting from industrialization. On the other hand, millions of tons of palm kernel shells (PKS) and other oil palm wastes are produced every year from oil palm downstream industries. In this study, we attempt to consolidate both problems, where the PKS was oxidized with sulfuric acid for the formation of PKS-Sulfo, where the oxygenated and sulfonated functional groups are attached to the activated carbon. The resulting PKS-Sulfo bio-adsorbent was characterized in detail and was used for the treatment of heavy metal-contaminated water. Different adsorption parameters; pH, concentrations of metal ions, contact time, and adsorbent dosage were optimized. It was found that the PKS-Sulfo bio-adsorbent is highly efficient in adsorbing heavy metal ions; Cr6+, Pb2+, Cd2+, and Zn2+ from their aqueous water solutions. The adsorption process was found to follow the pseudo-second-order model and the Langmuir isotherm was better fitted compared to the Freundlich adsorption isotherm for the adsorption process of the heavy metal ions. Furthermore, the adsorption capacities were also determined for all the metal ions were found to be 99% for Cr6+ and Pb2+ and Cd2+ and Zn2+ was found to be 80 % and 70% respectively. This study opens up a new horizon for the preparation of functionalized bio-adsorbents with the potential for numerous applications, especially for water remediation.

Environmental remediation and application of carbon-based nanomaterials in the treatment of heavy metal-contaminated water: A review

Nanotechnology is an advanced area of research that can solve a wide range of environmental issues by regulating the size and shape of materials on the nanometer scale. Because of their benign makeup, large surface area, ease of biodegradation, and special utility in environmental clean-up, carbon nanoparticles are exceptional. Around 25% of diseases that affect humans, according to the World Health Organisation, are caused by environmental pollution in the form of contaminated water, soil, and air. Among these, wastewater has been a major worldwide issue that has had a significant impact on many nations in different ways. Water contaminated with heavy metals is a serious issue that puts people's health at risk. Due to their exceptional physicochemical qualities that may be used for sophisticated treatment of heavy metal-contaminated water, carbon nanomaterials are gaining more and more attention. Due to their large surface area, nanoscale size, availability of various functionalities, and ease of chemical modification and recycling, carbon nanomaterials such as carbon nanotubes, fullerenes, graphene, graphene oxide, and activated carbon have great potential for the removal of heavy metals from water. The use of these carbon nanoparticles in treating water polluted with heavy metals has recently advanced, and we have examined these developments in this paper. We have also emphasised their use in environmental remediation. There has also been discussion of the toxicological concerns of carbon-based nanoparticles.

On As(III) Adsorption Characteristics of Innovative Magnetite Graphene Oxide Chitosan Microsphere.

A magnetite graphene oxide chitosan (MGOCS) composite microsphere was specifically prepared to efficiently adsorb As(III) from aqueous solutions. The characterization analysis of BET, XRD, VSM, TG, FTIR, XPS, and SEM-EDS was used to identify the characteristics and adsorption mechanism. Batch experiments were carried out to determine the effects of the operational parameters and to evaluate the adsorption kinetic and equilibrium isotherm. The results show that the MGOCS composite microsphere with a particle size of about 1.5 mm can be prepared by a straightforward method of dropping FeCl2, graphene oxide (GO), and chitosan (CS) mixtures into NaOH solutions and then drying the mixed solutions at 45 °C. The produced MGOCS had a strong thermal stability with a mass loss of <30% below 620 °C. The specific surface area and saturation magnetization of the produced MGOCS was 66.85 m2/g and 24.35 emu/g, respectively. The As(III) adsorption capacity (Qe) and removal efficiency (Re) was only 0.25 mg/g and 5.81% for GOCS, respectively. After 0.08 mol of Fe3O4 modification, more than 53% of As(III) was efficiently removed by the formed MGOCS from aqueous solutions over a wide pH range of 5–10, and this was almost unaffected by temperature. The coexisting ion of PO43− decreased Qe from 3.81 mg/g to 1.32 mg/g, but Mn2+ increased Qe from 3.50 mg/g to 4.19 mg/g. The As(III) adsorption fitted the best to the pseudo-second-order kinetic model, and the maximum Qe was 20.72 mg/g as fitted by the Sips model. After four times regeneration, the Re value of As(III) slightly decreased from 76.2% to 73.8%, and no secondary pollution of Fe happened. Chemisorption is the major mechanism for As(III) adsorption, and As(III) was adsorbed on the surface and interior of the MGOCS, while the adsorbed As(III) was partially oxidized to As(V) accompanied by the reduction of Fe(III) to Fe(II). The produced As(V) was further adsorbed through ligand exchange (by forming Fe–O–As complexes) and electrostatic attraction, enhancing the As(III) removal. As an easily prepared and environmental-friendly composite, MGOCS not only greatly adsorbs As(III) but also effectively removes Cr(VI) and As(V) (Re > 60%) and other metals, showing a great advantage in the treatment of heavy metal-contaminated water.

Using Biochar and Nanobiochar of Water Hyacinth and Black Tea Waste in Metals Removal from Aqueous Solutions

The treatment of heavy metal-contaminated water is challenging. The use of nanomaterials from many environmental wastes is promising for removing metals and contaminants from aqueous solutions. This study is novel in using nanobiochar of water hyacinth (WH) and black tea waste (TW) as a promising approach to water decontamination owing to its unique properties that play an effective role in metal adsorption. The mono- and multi-adsorption systems of cadmium (Cd), chromium (Cr), and nickel (Ni) on biochar and nanobiochar of water hyacinths (BWH and NBWH) and black tea waste (BTW and NBTW) were investigated in this study as potential low-cost and environmentally friendly absorbents for the removal of previously mentioned heavy metals (HMs) from aqueous solutions. The WH and TW were collected from the locality, prepared, and kept until used in the experiment. Nanobiochar was prepared by grinding, characterizing, and storing in airtight containers until used. A batch experiment was designed in mono- and competitive systems to study the adsorption equilibrium behavior of HMs on biochar and nanobiochars. The Freundlich and Langmuir isotherm models were fitted to the mono- and competitive-adsorption equilibrium results. The Freundlich isotherm model provided a better fit. Furthermore, it was noticed that NBWH and NBWT efficiently removed the Cd in the mono-system by ≥99.8, especially in the smaller concentration, while NBWT and BTW removed ≥99.8 and 99.7% in the competitive system, respectively. In the mono- and competitive systems, the nanobiochars of NBTW removed more than 98.8 of Cr. The sorbents were less efficient in Ni removal compared to Cd and Cr. However, their effectiveness was very high also. The results revealed that Cd was the highest metal removed by sorbents, nanobiochars were better than biochars to remove the HMs, and the results also indicated that co-occurrence of multi-metals might fully occupy the adsorption sites on biochars and nanobiochars.

Silk fibroin: a promising bio-material for the treatment of heavy metal-contaminated water, adsorption isotherms, kinetics, and mechanism.

Silk is the strongest natural biopolymer produced by silk worms possessing superior adsorbent properties and thus extensively used in various applications. The present study involved the preparation of powder form of a silk fibroin materials and their application in adsorption of heavy metals, particularly, iron from aqueous solution. The morphological and structural characteristic properties of this promising materialswere examined by using different analytical techniques. Batch experiments were conducted within feasible parametric ranges to understand the effect of dose, time, concentration, pH, and reusability. Silk fibroin was effective for iron adsorption over a wide range of pH 6 to 10. The adsorption removal efficiency of 98% was attained for removal of iron from contaminated water at moderate dose of 0.25g and contact time of 60min, which is unprecedented by considering the environment benign nature of the material. The data was examined in different isotherm models wherein it fitted best in Langmuir adsorption model. Similarly, Langmuir isotherm model, with R2 value of 0.984 and KL 0.412 and maximum adsorption capacity as 12.82mgg-1, suggests monolayer adsorption. Kinetic study with better R2 value of 0.941 represented the pseudo-second order kinetics governed by the chemisorption reaction. To understand the practical applicability of silk fibroin, the repeatability study up to 5 cycles were performed. The findings are very encouraging which confirmed the usage of silk fibroin as adsorbent for multiple cycles with marginal decrease in adsorption efficiency. Eventually, the material was tested for iron removal in real contaminated water which revealed its potential and selectivity for removal of iron in different matrix.

Functionalized Activated Carbon Derived from Palm Kernel Shells for the Treatment of Simulated Heavy Metal-Contaminated Water.

Heavy metal contamination in water poses a great risk to human health as well as to the lives of other creatures. Activated carbon is a useful material to be applied for the treatment of heavy metal-contaminated water. In this study, functionalized activated carbon (FAC) was produced by the induction of nitro groups onto activated carbon using nitric acid. The resulting material was characterized in detail using the XRD, Raman, BET, FTIR, and FESEM techniques. The FAC was used for the treatment of heavy metal-contaminated water using different adsorption parameters, i.e., solution pH, contact time, adsorbent dosage and heavy metal ion concentrations, and these parameters were systematically optimized. It was found that FAC requires 90 min for the maximum adsorption of the heavy metal ions; Cr6+, Pb2+, Zn2+ and Cd2+. The kinetic study revealed that the metal ion adsorption follows the pseudo-second-order. The Freundlich and Langmuir isotherms were applied to determine the best fitting adsorption isotherm models. The adsorption capacities were also determined for each metal ion.

Effectiveness of discarded cigarette butts derived carbonaceous adsorbent for heavy metals removal from water

Disposed cigarette butt is one of the biggest solid, non-biodegradable wastes across the world. Cigarette butts (CBs) made of cellulose acetate are good candidates for the initial raw materials of carbon materials synthesis, providing a possible way for waste CBs recycling. Herein a carbonaceous adsorbent derived from waste CBs was prepared for the heavy metals removal from aqueous solution. The product activated at 500 °C has a maximum adsorption capacity for lead ions, which has a favorable balance of high specific surface area and abundant O-containing functional groups, facilitating the adsorption of heavy metals ions. The adsorption experiments showed that the pH of the solution played a pivotal role in the adsorption of heavy metals by CBs-derived activated carbons and the optimal pH for the adsorption was around 5. Effective adsorption of chromium (Cr3+), cobalt (Co2+), nickel (Ni2+), lead (Pb2+) and cadmium (Cd2+) demonstrated that the prepared materials can be used for multiple heavy metal ions removal. The prepared materials were able to adsorb Pb2+ within ten minutes, and the adsorption process can be well described by the pseudo-second order model, indicating that the chemical adsorption is the rate determining step for the adsorption process. The equilibrium data followed the Langmuir isotherm model and the corresponding maximum adsorption capacity for Pb2+ was 249.3 mg g−1. Considering the merits of low cost, easy synthesis pathway and excellent removal ability of heavy metals, CBs-derived carbonaceous adsorbent exhibits potential application in the fields of heavy metal contaminated water treatment.

Facile synthesis and applications of carbon nanotubes in heavy-metal remediation and biomedical fields: A comprehensive review

Carbon nanotubes (CNTs) have drawn great attention due to the rich science underpinning their applications coupled with a unique combination of properties like large aspect ratios, superior thermal and electrical conductivity, excellent optical characteristics and high surface area. Through chemical modification, re-engineering and functionalization, control of parameters such as surface chemistry, size distribution, surface area, agglomeration and structure have been made possible leading to improved functionality. CNTs not only holds promise in a wide range of applications in medicine, nano and microelectronics, and environmental remediation but can also be used for laboratory experimental tenacities. More particularly, CNTs serve as an excellent adsorbent in the removal of heavy metal ions (HMI) from wastewater. Equally, they are capable of coupling with many therapeutic and diagnostic agents hence being used in biomedical applications such as tissue engineering, cancer therapy, drug delivery, biosensing and imaging. These two distinguished and noble applications have offered improved human health services and ensured a safer environment thus momentously revolutionizing human life. In that regard, this article has reviewed the advancements in the applications of CNTs in the treatment of heavy metal-contaminated water and biomedical applications drawn from several research articles and other publications.

Efficient removal of selenate in water by cationic poly(allyltrimethylammonium) grafted chitosan and biochar composite

The discovery of cheap and eco-friendly functional materials for the removal of anionic heavy metal ions is still challenging in the treatment of heavy metal-contaminated water. Herein, a new poly(allyltrimethylammonium) grafted chitosan and biochar composite (PATMAC-CTS-BC) was introduced for the removal of selenate (SeO42−) in water. Results suggest that the PATMAC-CTS-BC showed a rapid removal of SeO42− with efficiency of >97% within 10 min and it followed a pseudo-second-order model. High capacity of SeO42− adsorption by the composite was achieved, with maximum value of 98.99 mg g−1 based on Langmuir model, considerably higher than most of reported adsorbents. The thermodynamic results reflected the spontaneous and exothermic nature of SeO42− adsorption onto the composite. The composite could be applied at a wide initial pH range (2–10) with high removal efficiency of SeO42− because of permanent positive charges of quaternary ammonium groups (=N+–). The removal mechanisms of SeO42− were mainly attributed to electrostatic interactions with =N+– and protonated –NH3+ groups, and redox-complexation interactions with –NH2, –NH–, and –OH groups. Besides SeO42−, the hexavalent chromium (Cr2O72−) was considered as example to further demonstrate the anion removal capability of cationic hydrogel-BC composite. The study outcomes open up new opportunities to efficiently remove anionic heavy metal ions (e.g., SeO42− and Cr2O72−) in water using these materials.

Ecofriendly Approach for Treatment of Heavy-Metal-Contaminated Water Using Activated Carbon of Kernel Shell of Oil Palm.

Heavy metal ion contamination in water poses a significant risk to human health as well as to the environment. Millions of tons of agricultural wastes are produced from oil palm plantations which are challenging to manage. In this study, we converted palm kernel shells (PKS) from a palm oil plantation into activated carbon (AC) having a surface area of 1099 m2/g using phosphoric acid as an activator. The prepared material was characterized using BET, XRD, Raman, FESEM and FTIR analyses. The AC was applied for the treatment of heavy-metal-contaminated water, and different parameters; the pH, adsorbent dosage, contact time and metal ion concentrations were varied to determine the optimal conditions for the metal ion adsorption. Different kinetic models; the zeroth, first-order and second-order, and Freundlich and Langmuir isotherm models were used to determine the mechanism of metal ion adsorption by the AC. Under the optimized conditions, Cr6+ and Pb2+ were removed completely, while Zn2+ and Cd2+ were more than 80% removed. This is a greener approach in which an agricultural waste, PKS is converted into a useful product, activated carbon and subsequently applied for the treatment of heavy metal-contaminated water.

High-dispersion zero-valent iron particles stabilized by artificial humic acid for lead ion removal

Nano zero-valent iron (nZVI), as a high-efficiency adsorbent for heavy metals, often suffers being oxidized and assembling together due to small size and super reactivity, further decreasing its adsorption performance and limiting application ranges. Herein, we have designed a novel adsorbent with high-dispersion nZVI stabilized by as-prepared artificial humic acid (AHA-nZVI) derived from hydrothermal humification (HTH) technology. Introduction of artificial humic acid (A-HA) can effectively reduce the oxidation and agglomeration of nZVI, leading to superior kinetic removal efficiency of Pb2+ (> 99.2%) and huge Langmuir removal capacity of 649.0 mg/g. The combination of nZVI and A-HA (contained abundant functional groups, i.e. −OH and −COOH) via C–O-Fe bonding makes nZVI have good dispersion and oxidation resistance. Multiple interaction mechanisms including reduction reaction, complexation and co-precipitation between heavy metals and AHA-nZVI samples are realized. Overall, AHA-nZVI is a promising material for high-performance heavy metal contaminated water treatment.

PEI modified multiwalled carbon nanotube as a novel additive in PAN nanofiber membrane for enhanced removal of heavy metal ions

Both multiwalled carbon nanotubes (MWCNTs) and electrospun nanofibers are ideal nanomaterial candidates with great potential in the field of heavy metal ions remediation. In the present study, the advantages of these two nanomaterials were combined with electrospinning method to prepare a novel nanocomposite membrane (NCM) containing improved physical properties and enhanced removal efficiency for metal ions. Modified MWCNTs were initially fabricated by reacting MWCNT-COOH with polyethylenimine (PEI), which was further embedded within polyacrylonitrile (PAN) nanofibers through electrospinning. The structure, morphology and physical property of prepared MWCNT-PEI and NCM (MWCNT-PEI/PAN) were carefully characterized with FTIR, SEM, TEM, mechanical test and contact angle measurements. Compared with plain PAN membrane, the prepared NCM possesses higher mechanical strength and improved hydrophilicity, resulting in high permeation and filtration efficiency. Batch adsorption experiments demonstrated that MWCNT-PEI/PAN nanocomposite membrane exhibited higher adsorption amount for Pb2+ and Cu2+ ions compared with other nanocomposite membranes. Additionally, the adsorption processes were elaborated to follow pseudo-second-order kinetic and Langmuir isotherm, indicating the PEI groups embedded in the NCM was the main adsorption active site and chemisorption was the mainly mechanism for the uptake of heavy metal ions. The dynamic adsorption results proved that the designed NCM exhibited improved rejection ability to metal ions with a water flux at 145.8 L m−2 h−1 under 0.2 bar pressure. The NCM could treat 240 mL and 170 mL of 40 mg/L Cu2+ and Pb2+ solution while maintaining a drinking water standard of 1 mg/L and 10 µg/L, respectively. The improved membrane performance along with the excellent heavy metal removal efficiency suggests that this novel prepared NCM possess promising potential for heavy metal contaminated water treatment through the process of membrane adsorption.

The removal of Pb (II) and Cd (II) with hydrous manganese dioxide: mechanism on zeta potential and adsorption behavior

ABSTRACT In this study, the removal of Pb (II) and Cd (II) in aqueous solution by employing hydrous manganese dioxide (HMO) is investigated. The HMO synthesized was characterized by SEM, XRD, BET, FT-IR, and XPS. Simultaneously, the effect of Zeta potential (ZP), solution pH and contact time were discussed. The results reveal that at pH 5.0, 1-HMO (−51.7 mV) with the highest |ZP| value can reach equilibrium and reach 95.7% removal rate within 30 mins. The isotherm and kinetic data fitted Langmuir and pseudo-second-order models well. The maximum adsorption capacities calculated by Langmuir equation are 475.4 mg/g for Pb (II) and 140.3 mg/g for Cd (II) at 303.15 K, respectively. The binary experiment indicates the HMO showed a better affinity for Pb (II) than Cd (II). Thermodynamic studies (ΔG < 0, ΔH > 0, ΔS > 0) implies the both adsorptions are endothermic and spontaneous process. The intraparticle model analysis indicates that the film discussion controls the metal ions adsorption at the earlier stage and the intraparticle diffusion at the middle stage, while a chemical bonding process at the equilibrium stage. The FTIR and XPS analysis further proves Pb (II) and Cd (II) being adsorbed onto the surface of HMO as Pb-O and Cd-O, resulting from ion exchange and complexation. The reacted HMO could be recycled and reused for several times in a high efficiency above 90% by adding HCl or new HMO adsorbent. Simple preparation, low cost and remarkable removal efficiency make HMO a promising material in the treatment of heavy metal-contaminated water.

Decomplexation of Cu(II)-EDTA over oxygen-doped g-C3N4: An available resource towards environmental sustainability

Photocatlytic decomplexation provides an effective way to tackle the problem of heavy metal contamination. By far, the exploration of more efficient photocatalysts with low environmental risk is still an important but challenging issue. In this study, the feasibility of using metal-free carbon nitride as environmental-friendly catalysts for photocatalytic decomplexation was demonstrated, using Cu(II)-EDTA as a model contaminant. A facile oxygen doping strategy could significantly enhance the interfacial separation of photogenerated holes, which was determined to be the most effective reactive species for decomplexation reactions. Compared to pristine g-C3N4, oxygen doped sample exhibited 2.5-fold enhanced photoactivity. The hypothesis of using decomplexation solution as sustainable resource for fabricating copper modified photocatalysts was further investigated. The in-situ formation of Cu or Cu2O resulted in the significantly improved activity for hydrogen evolution over recycled photocatalysts. According to the component analysis, chemical reduction strategy was beneficial for the sufficient recovery of copper ions, while the photoreduction method led to the most efficient utilization of copper metals. This study not only presents a promising method for the treatment of heavy metal-contaminated water, but also provides a sustainable way to utilize decomplexation solution as valuable resource for clean energy production.

Ternary carboxymethyl chitosan-hemicellulose-nanosized TiO2 composite as effective adsorbent for removal of heavy metal contaminants from water

A ternary composite consisting of carboxymethyl chitosan, hemicellulose, and nanosized TiO2 (CHNT) was prepared by incorporating TiO2 nanoparticles into the pre-synthesized carboxymethyl chitosan-hemicellulose polysaccharide network. The microstructure and chemical composition of the obtained CHNT was characterized by TEM, SEM, FTIR, and TGA. The adsorption of some toxic heavy metals including Ni(II), Cd(II), Cu(II), Hg(II), Mn(VII), and Cr(VI), onto the as-prepared CHNT composite was investigated. The effects of pH, temperature and contacting time on the adsorption process were studied. Results revealed that the CHNT composite exhibited efficient adsorption capacity of the above metal ions from aqueous solution due to its favorable chelating groups in structure. The adsorption process was best described by the pseudo-second-order kinetic model, while isotherm modeling revealed that the Langmuir equation better described the adsorption on CHNT as compared to Freundlich model. Moreover, the CHNT loaded metal ions can be easily regenerated with EDTA and reused repeatedly up to five cycles. The environmental friendly hybrids were expected to be a promising candidate for future practical application in heavy metal contaminated water treatment.

Hierarchical porous hydroxyapatite microspheres: synthesis and application in water treatment

Hydroxyapatite (HA) microspheres with hierarchical porous structure were synthesized using a facile gas diffusion method. The morphology and structure of the as-synthesized products were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, scanning electron microscopy, and Brunauer–Emmett–Teller gas sorptometry analyses. Results showed that the change in pH resulting from ammonia diffusion provided the driving force for the formation of HA crystals. Under the cooperative influences of reaction time and reaction temperature, the nucleation and growth processes of HA nanocrystals were effectively controlled. Therefore, porous HA microspheres with large surface areas were produced at 60 °C for 24 h. On the basis of the time-dependent experiments, a possible formation mechanism of hierarchical porous HA microsphere was proposed. Moreover, hierarchical porous HA microspheres were investigated as adsorbent, and they exhibited a high adsorptive capacity for heavy metals Pb2+ and Cu2+ of approximately 213.58 ± 2.6375 and 59.68 ± 3.4436 mg/g, respectively. Therefore, hierarchical porous HA microspheres may be applied to heavy metal-contaminated water treatment.