In this work, molecular dynamics (MD) simulations were applied to address the major concerns about the independent and competitive adsorption processes of phenolic organic pollutants (POPs) on the graphene oxide (GO) in aqueous solution. Phenol, α-naphthol and 4-octyl-phenol were adopted as representatives of POPs and their adsorption energies were calculated, which followed an order of 4-octyl-phenol (41.34 kJ/mol)>α-naphthol (33.23 kJ/mol)> phenol (19.31 kJ/mol). The simulation results showed that hydrophobic properties of POPs were recognized as the driving force for their adsorption behaviors. Moreover, van der Waals interaction, electrostatic interaction, as well as hydrogen bonds, may also improve the adsorption capacity of GO towards POPs. The competitive adsorption process revealed that in addition to the direct adsorption onto the GO surface, the molecular aggregation may be another indirect adsorption way existed in the mixed system. Understanding the interaction between GO and POPs in aqueous solution is critical to the design and application of graphene-based materials and our findings are believed to contribute further theoretical basis to the engineering treatment of POPs-containing waste water.

In present work, a systematical and comprehensive understanding for the adsorption of Cd(II) on porous hexagonal boron nitride (p-BN) was studied. The chemical compositions, morphology and surface functional groups of p-BN before and after adsorption were characterized by SEM, HRTEM, BET, XRD, and FT-IR. The effects of pH, adsorbent dosage, contact time and temperature on Cd(II) adsorption were investigated. The maximum adsorption capacity for Cd(II) achieves 184 mg·g -1 at pH 7.0 and 313 K. The kinetic data fitted well with pseudo-second-order model and intra-particle diffusion model, indicating that the adsorption is mainly controlled by chemisorption, and the rate-limiting step is the molecular diffusion. The adsorption isotherms are in accordance with Freundlich and Langmuir model respectively, suggesting Cd(II) adsorbed on the heterogeneous surface through multilayer and monolayer adsorption. The thermodynamic parameters are calculated to confirm the spontaneous and endothermic process of Cd(II) sorption. Spectroscopic results from XPS imply that p-BN adsorbent had substantial functional groups and bonding sites, which is propitious to uptake Cd(II) from wastewater. These results revealed that p-BN is a promising candidate for Cd(II) scavenging.

Herein, the retention mechanisms and microstructure of Cd(II) on MoS2 nanosheets were evaluated by batch experiments and EXAFS technology. The sorption of Cd(II) on MoS2 was strongly affected by solution pH, contact time, and temperature, but not by the ionic strength. The solution pH could only promote the sorption capacity, but does not improve the sorption rates and change the sorption isotherms and thermodynamics in the pH range of 3.3-9.6. The pseudo-second-order model could fit the equilibrium data better and the intra-particle diffusion model showed three typical stages in the sorption process. The isotherms and thermodynamics analysis indicated that the heterogeneity sorption of Cd(II) onto MoS2 was a spontaneous, endothermic, and irreversible process. The EXAFS spectra revealed the coexistence of two sorption types. The inner-sphere complexation was formed in the form of Cd-S bond at lower pH (3.56, 6.48), while the Cd(OH)2 precipitation occurred in the form of Cd-O and Cd-Cd bonds at higher pH (9.57). These results provide new insights into the interaction mechanisms between metal ions and MoS2 nanosheets.

Heavy metal chromium pollution seriously threatens the environmental safety of soil and water body. The Cr(VI) compound has strong migration ability, enrichment and strong oxidizing ability. These properties make Cr(VI) ions more dangerous and difficult to handle. Adsorption technology is a simple and effective method for treatment of heavy metal pollution. The two clay-biochars are made by mixing biochar derived from peanut shell and two kinds of clays (Kaolin and bentonite) under magnetic stirring conditions. A variety of characterizations suggest that clays uniformly deposit on the surface of biochar. Adsorption experiments indicate that the sorption of Cr(VI) ions from wastewater on Kaolin-biochar is significantly higher than that of bentonite-biochar. Adsorption kinetic of Cr (VI) on two clay-biochars follows satisfactorily the pseudo-second order model due to high correlation coefficient (R2>0.999). Adsorption isotherms of Cr(VI) on Biochar@Bentonite are fitted by Langmuir model, whereas the Freundlich model fits better the Cr(VI) sorption on Biochar@Kaolin. These findings are crucial for the potential application of clay-biochar composites for the treatment of the immobilization of heavy metals in environmental remediation.

Cr(VI) is toxic to the organic life. Eliminating the pollutant of Cr(VI) in solution has become a hot research field. In this work, the C@K2Ti6O13 hierarchical nanomaterials were prepared by liquid phase deposition combined with hydrothermal treatment, which were constituted by carbon nano spheres and K2Ti6O13 nanobelts. The morphology and phase of the materials were characterized by different methods. The C@K2Ti6O13 hierarchical nanomaterials show high potential as adsorbent to adsorb Cr(VI). Effect of initial pH, adsorption time and ionic strength on Cr(VI) adsorption by C@K2Ti6O13 composite nanostructures were investigated. The elimination rate of Cr(VI) can reach 50% in 1 h. The adsorption kinetics agrees well with the pseudo- second-order kinetic model, and the adsorption thermodynamics accords with the Langmuir isotherm adsorption model. It can be expected that the C@K2Ti6O13 hierarchical nanomaterials have great application potential in environmental treatment.

A low-cost oyster shell was carried to prepare biogenic calcium carbonate (bio-CaCO3) to remediate Pb(II) and methyl orange (MO) from contaminated water. The morphology, composition and structure of the material were analyzed mainly by scanning electron microscope (SEM), thermogravimetric analysis (TGA), X-ray fluorescence (XRF). The adsorption of Pb(II) and MO by bio-CaCO3 was studied by combining batch experiments and microstructure characterization. Batch sorption experiments showed that 45% MO was removed by bio-CaCO3 (msorbent/Vsolvent=0.2 g/L, [MO]initial=60 mg/L). An obviously morphology change took place after MO adsorbed onto bio-CaCO3. The maximum sorption capacity of bio-CaCO3 for Pb(II) is 1775 mg/g (pH=5.0, T=298 K), which is higher than that of the traditional nanomaterials such as bentonite and activated carbon. The Pb(II) removal mechanism is expected to be CaCO3+ Pb(II)→PbCO3, where the ΔHθ, ΔSθ and ΔGθ of Pb(II) sorption by bio-CaCO3 (pH=5.0, T=298K) are -7.64 kJ/mol, -17.92 J/(mol·K) and -2.30 kJ/mol, respectively. More regular products with quadrangular structure are formed after Pb(II) adsorption. The results highlight that the bio-CaCO3 has a high Pb(II) and MO sorption efficiency, demonstrating that it is a promising adsorbent material in environmental pollution management.

As a narrow band gap semiconductor, Bi2WO6 has great application potential in photo-degradation of organic pollutants, such as tetracycline. In present work, Bi2WO6 nanosheets were successfully synthesized by a hydrothermal method and the photo-degradation of tetracycline under visible light irradiation were investigated. XRD, FESEM, TEM and absorption spectra were used to characterize the structure and morphology of the material. It was found that when adding 50 mg Bi2WO6 nanosheets into 50 mL of tetracycline solution at pH=8, 85% tetracycline (50 mL, 50 mg/L) was photodegraded within 130 min. The photoelectron-chemical experiments and free radical capture experiments were performed to explore the photo-degradation mechanism. The results show that good photocatalytic performance of Bi2WO6 nanosheets are ascribed to the high electron density and photoelectron-hole separation efficiency.

Persistent organic pollutants can be effectively removed by photocatalytic oxidation, which reveals potential application prospects in the field of wastewater purification. Binary reduced graphene oxide and graphitic carbon nitride (RGO/g-C3N4) visible-light photocatalyst was successfully fabricated by the freeze drying assisted thermal polymerization method with urea and dicyandiamide as raw materials, respectively. The morphologies, structures and optical properties were characterized by various techniques. It was found that g-C3N4 and RGO nanostructures formed an intimate contact across the heterojunction interface. The photodegradation performances of catalysts were evaluated by removing bisphenol A (BPA) with the activation of persulfate (PS). The results indicated that the photocatalytic activities of photocatalysts were enhanced with the addition of PS as an oxidant and electron acceptor under visible light irradiation (λ>420 nm). Moreover, BPA was almost completely removed by RGO/g-C3N4 prepared with urea as raw material in 40 min. After five recovery tests, the removal efficiency of BPA for the catalyst was up to 80% within 40 min under visible light irradiation, which exhibited superior stability.

Boron is an important micronutrient for plants, animals, and humans. However, high concentrations of boron are harmful to animals and plants. A magnesium-aluminum-cerium hydrotalcite (Mg-Al-Ce-HT) was successfully prepared by the co-precipitation method for boron removal. Different analyses were conducted to confirm the structure and characteristics of Mg-Al-Ce-HT. Adsorption efficiency of Mg-Al-Ce-HT was studied as a function of initial pH, amount of adsorbent, concentration of initial boric acid, and contact time. The pH of the solution had a negligible effect on boron sorption when pH was less than 8.0. However, the adsorption capacity decreased when the pH exceeded 8.0. The optimum amount of the adsorbent was 200 mg, and the maximum adsorption capacity was 32.52 mg·g -1. Boron removal reached equilibrium at 160 min. The thermodynamic parameters revealed that the adsorption was a non-spontaneous and endothermic process. The data fitted well with the Langmuir model, which indicated that the process involved monolayer adsorption.

Radioactive iodine present in nuclear waste water streams is harmful to human health and environment. Since iodine will exist in multiple states in water, accurate quantification of the total iodine content in any given sample is very difficult. The development of a method for determining the total iodine content accurately in water, and finding materials which can effectively remove the iodine are of particular importance. Here, a method was proposed for determining the concentration of iodine by cyclohexane extraction. And two kinds of zeolite imidazole skeleton materials ZIF-8 and ZIF-67 were prepared to be used as adsorbents to effectively adsorb iodine from an aqueous environment. Samples ZIF-8 and ZIF-67 were characterized by different methods. The results show that these two kinds of materials have good chemical structure and large specific surface area. The results of adsorption kinetics experiments show that the adsorption of ZIF-8 and ZIF-67 materials to iodine can reach the equilibrium within 60 min. The iodine adsorption behaviors of both materials are fitted with the pseudo second-order kinetic model. Their adsorption thermodynamics indicate linear adsorption behavior for iodine in the case of both zeolites. Adsorption capacities of ZIF-8 and ZIF-67 for iodine could reach as high as 2000 mg·g -1.

Hydrothermal carbon adsorption materials possess the advantages of simple preparation process, mild synthesis conditions and easy surface modification. In this UO22+speciation as a function of CO32- concentration, soluble starch used as carbon source, acrylonitrile was grafted onto starch molecule through ring opening under the catalysis of cerium ammonium nitrate. Subsequently, amidoxime hydrothermal carbon spheres (AO-HTC) were successfully synthesized by hydrothermal reaction and hydroxylamine hydrochloride reduction. Meanwhile, static and dynamic adsorption experiments were performed to investigate the effects of solution pH, carbonate and calcium ion concentration on the adsorption performance of AO-HTC for uranium. And the dynamic adsorption process of AO-HTC for uranium was also studied by Yoon-Nelson and Thomas models. The results show that the adsorption capacity of AO-HTC, the volume of penetration point as well as saturation point in the penetration curve also decreases gradually with the increase of pH, carbonate concentration and calcium concentration. The maximum adsorption capacity (qo) and the required time (τ) of adsorbate through 50% of 5% AO-HTC column are several times higher than that of pure soil column. Therefore, the research highlights that AO-HTC would act as an excellent permeable-reactive barriers (PRB) medium and expected to remediate uranium-contaminated soil and groundwater.

Reduction of soluble U(VI) to insoluble U(IV) oxide is an effective approach to control uranium contamination. Three-dimensional (3D) macroporous g-C3N4 photocatalyst with interconnected porous was prepared by thermal polymerization and template etching using self-assembly of SiO2 nanosphere as the template. The material was then applied to adsorption-photocatalytic reduction of U(VI). Characterization results showed that the 3D macroporous g-C3N4 photocatalyst presented a well-defined interconnected macroporous architecture and numerous nanopores existed on the well-defined macroporous skeleton. 3D macroporous g-C3N4 also had a significant increase in specific surface area which was beneficial to the absorption of visible light. Adsorption results showed that the maximum adsorption capacity of U(VI) on 3D macroporous g-C3N4 was ~30.5 mg/g, which was more than ~1.83 times higher than that of bulk g-C3N4. The adsorption isotherm matched well with the Langumuir equation. Photocatalytic reduction experiments showed that the 3D macroporous g-C3N4 had high photocatalytic activity and good stability with the reduction rate constant of 0.0142 min -1, which was ~4.9 times higher than bulk g-C3N4 (~0.0024 min -1). As the sorption-photocatalytic performance of the sample is excellent, 3D macroporous g-C3N4 is a high efficient visible-light-responsive photocatalyst for the removal of U(VI) from radioactive wastewater.

137Cs is one of the most intractable β-emitters which is commonly generated from nuclear weapons test and nuclear power station. Due to the nature of high solubility and mobility, the effective sequestration of 137Cs + from radioactive waste solution is considered as a long-term challenge. In this work, a two-dimensional layered anion framework material (SZ-6) was synthesized through conventional solvothermal reaction and the Cs + removal properties were systematically investigated. Single Crystal X-ray Diffraction (SCXRD) analysis revealed that SZ-6 adopts layer packed structure with large tetramethylammonium cations loaded between the layers which is greatly beneficial to cation exchange process. Powder X-ray Diffraction (XRD) and Scanning Electron Microscope (SEM) confirmed the material with high purity and excellent hydrolytic stability. Batch experiments were used to investigate the adsorption behavior towards Cs + in aqueous solutions. The adsorption kinetics of SZ-6 could be achieved within 5 min, which is currently one of the fastest sorbents for the removal of Cs +. Meanwhile, SZ-6 exhibits superior decontamination capability over a wide pH range from 4 to 12. Furthermore, it possesses marked selectivity in the presence of large excess of Na +, K +, Ca 2+ competing cations.

With the development of nuclear power, radioactive pollutants discharge into the environment and then contaminate soil and water resources. Nanoscale zero-valent iron (nZVI) materials are widely used in water remediation due to their strong reducibility and high removal efficiency. A carbon-based zero-valent iron material (Fe-CB) was prepared in this work. Fe-CB was fabricated using sodium alginate (SA) as a carbon source via one-step carbothermic method and then applied to eliminate U(Ⅵ) from aqueous solution. Its mechanism and adsorption properties of Fe-CB and U(VI) were studied by spectroscopic analyses and macroscopic experiments. The results illustrated that Fe-CB possessed of ample functional groups (such as -OH and -COOH) and high BET surface area, which made up for the dispersibility and low removal efficiency of nanoscale zero-valent iron (nZVI). The removal of U(VI) by Fe-CB achieved equilibrium in 3 h and the maximum sorption capacity was 77.3 mg·g -1 at 298 K. XPS analyses indicated that the U(Ⅵ) removal by Fe-CB was a synergistic effect of reductive adsorptive processes. Adsorption process resulted from surface complexation and the reduction process was dominated by U(VI) reduction to U(IV) by nZVI. The results show that Fe-CB can be used as an inexpensive and highly efficient pollutant scavenger, which has great potential for environment pollution management.

Nanoscale zero-valent iron (NZVI) has been widely applied to eliminate radionuclide U(VI). However, poor stability and low efficiency restrict the employment of pure NZVI. In this study, surface passivation and dispersion technology were employed together. Ca-Mg-Al layered double hydroxide supported sulfide NZVI (CMAL-SNZVI) was synthesized and applied for U(VI) elimination. Macroscopic and microscopic investigations demonstrate the outstanding physicochemical properties, high reactivity and excellent performance for U(VI) removal. The reaction process can be achieved equilibrium within 2 h and the maximum elimination capacity reaches 175.7 mg·g -1. The removal mechanism of U(VI) on CMAL-SNZVI is the synergistic effect between adsorption and reduction, through which U(VI) can be adsorbed by CMAL base and the SNZVI surface via inner-sphere surface complexation, U(VI) can be reduced into less toxic and insoluble U(IV) by Fe 0 inner core. Overall, the synthetization of CMAL-SNZVI can lead a new direction of NZVI modification. In the meantime, the outstanding performance of U(VI) removal indicate the potential of CMAL-SNZVI as excellent material for environment remediation.

Biochar, derived from agricultural residuals, is extensively applied to remove detrimental heavy metals from wastewater, which has dual significance for the environment protection. Herein, the sorption behavior and interaction mechanism of Eu(III) on rice straw-derived biochar was investigated by batch and spectroscopic technologies. The solution pH significantly affects the percentage of the sorption, but has little effect on the contact time. Humic substances (HA/FA) significantly enhance Eu(III) sorption with solution pH7.0. The sorption mechanism involves co-precipitation or inner-sphere surface complexation. And the chemical sorption rate is restricted by intra-particle diffusion process. Besides, the Freundlich model simulates isotherms best and the maximum sorption amount is up to 40.717 mg/kg, which correlates with the stratified structure and abundant functional groups of biochar. The thermodynamic parameters suggest that the sorption of Eu(III) on biochar is a spontaneous and endothermic process. Therefore, these results are valuable to assess the potential application values of rice straw-derived biochar for the removal of Eu(III) in water systems.

Graphitic-like carbon nitride (g-C3N4), one of the most significant two-dimensional layered materials, has attracted worldwide attention in multidisciplinary areas such as photocatalysis, energy conversion and environmental pollution management. Its derivative compounds have also attracted multifarious attention owing to the intrinsic characters of their stable physicochemical properties, low cost and environmentally friendly features. This review focus on the design of high-performance g-C3N4-based nanomaterials and their potential for pollutant elimination in environmental pollution cleanup. Over the past few years, significant advances have been achieved to synthesize g-C3N4 and g-C3N4-based nanomaterials, and their properties have been enhanced and characterized in detail. In this review, recent developments in the synthesis and modification of g-C3N4-based nanomaterials are summarized. The applications in heavy metal ions adsorption from wastewaters are gathered and their underlying reaction mechanisms are discussed. Finally, a summary and outlook are also briefly illustrated.

For the future advanced nuclear fuel cycle system, pyrochemical technology based on molten salt electrolysis is generally considered to be one of the most promising and reliable reprocessing technologies. The salt-containing waste generated in each step of the pyrochemical process needs to be converted into a ceramic waste form, which can be stably disposed in a long term manner in deep geological repository. This is of pivotal importance for the scale-up and industrialization of molten salt electrolysis based pyrochemical processing. In this review, the current research progresses of ceramic solidification technology in main nuclear energy countries with respect to salt-containing wastes were summarized and reviewed, with emphasis on ceramic solidifications of salt-containing wastes from electro-reduction process in LiCl-based salt and electro-refining process in LiCl-KCl salt. In addition, future perspectives in this field are also given.