With the development of nuclear energy, the long-lived radionuclides are inevitably released into the natural environment during the mine process, fuel manufacture, nuclear power usable and spent fuel management, which are dangerous to human health and environmental pollution. Thereby the efficient elimination of radionuclides is an important parameter which affects the development of nuclear power. In recent years, the metal-organic frameworks (MOFs) have attracted worldwide attention in the adsorption of radionuclides from large volume of aqueous solutions, because of their high chemical stability, abundant functional groups and changeable porous structures. In this review, we mainly summarized the recent works of MOFs in the efficient removal of radionuclides, and to understand the interaction mechanism from batch adsorption experiments, model analysis, advanced spectroscopy analysis, and theoretical calculation. The adsorption capacities of MOFs with other materials were also summarized, and the future research opportunities and challenges are given in the perspective.

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, signi?cant 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.

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.

Photocatalyst of N-doped Bi₂O₂CO₃ (N-BOC)/CdSe quantun dots (QDs) composite was sucessfully prepared for degradation of nitric oxide (NO), an indoor air pollutant. The results of X-ray diffraction, transmisssion electron microscopy and X-ray photoelectron spectroscopy showed that after combination with CdSe QDs structure and morphology of N-BOC remained the same as before combination. Photocatalytic degradation of NO showed that introduction of CdSe QDs significantly enhanced the removal ratio of NO. Moreover, the generating ratio of toxic byproduct NO₂ decreased to 1%, which indicated efficient inhibition for the toxic byproduct generation. From UV-Vis absorption spectroscopy and photoluminescence spectroscopy, the CdSe QDs showed promotion on light absorption, and inhibition of charged recombination of photo-induced carriers. More importantly, only signals of NO₃ ^- were captured in in situ DRIFTS measurements, whilst the signals from NO₂ could be barely detected during photocatalytic process. Superoxide radicals (O₂ ^-) and holes (h ⁺) are considered to be possible active species in the reaction, which dominate the oxidation process from NO to NO₃ ^-.

Photocatalysis technology possesses great potential in the field of oxidation of nitrogen oxides due to the low energy costs and little secondary pollution. Bismuth carbonate (Bi₂O₂CO₃, BOC)/polypyrrole (PPy) was prepared at room temperature to remove NO under visible light irradiation. After being decorated with PPy, the NO removal efficiency of BOC is enhanced from 9.4% to 20.4% while the generation of NO₂ is reduced from 2% to approximately zero, which are attributed to the oxygen vacancy formed at the interface between BOC and PPy via interfacial hydrogen bonding. Photocurrent and electrochemical impedance spectra indicate that oxygen vacancies promote the separation and migration of photo-induced electrons and holes over BOC, hence improve its photocatalytic activity. Furthermore, the presence of oxygen vacancy promotes the formation of more •O₂ ^-, and then improve the NO oxidation activity and safety of BOC together with •OH.

Given the good electrochemical performance and excellent irradiation stability of two dimensional transition metal carbides (MXenes), the development of MXene-based electrode materials for radionuclide detection is very promising. In this work, Ti₃C₂T_x MXene was activated via an alkalization strategy to form K⁺ intercalated Ti₃C₂T_x (K-Ti₃C₂T_x). Then the modified electrode of K-Ti₃C₂T_x/GCE was prepared on glassy carbon electrode (GCE). Ti₃C₂T_x and K-Ti₃C₂T_x were characterized by XRD, SEM and XPS techniques, and the electrochemical detection performance of K-Ti₃C₂T_x/GCE for trace uranyl ion (UO₂²⁺) was further investigated. Cyclic voltammetry (CV) experiments showed that the electrochemical response of K-Ti₃C₂T_x/GCE modified electrode to UO₂²⁺ increased significantly. Under the differential pulse voltammetry (DPV) scanning at pH 4.0, the K-Ti₃C₂T_x/GCE modified electrode presented a good linear detection relationship for UO₂²⁺ in the uranium concentration range of 0.5-10mg/L. The detection limit of this method is 0.083 mg/L (S/N = 3), with decent stability and repeatability.

In order to rapidly remove Eu(III) from aqueous solution, an alkalized two-dimensional titanium carbide, Na-Ti₃C₂T_x, was successfully prepared by treating inorganic two-dimensional transition metal carbide (MXene) with NaOH. Adsorption behavior of Eu(III) on Na-Ti₃C₂T_x was systematically investigated by batch experiments. The results show that the adsorption process is greatly affected by pH and ionic strength of the solution, and reached equilibrium within 5 min. Based on Langmuir model fitting results, the maximum adsorption capacity of Eu(III) on Na-Ti₃C₂T_x was calculated to be 54.05 mg/g at pH 4.0 under 298 K. The thermodynamic results suggested that the adsorption process was a spontaneous and endothermic reaction. The adsorption mechanism was further analyzed by energy dispersive X-ray spectroscopy (EDS), powder X-ray diffraction (XRD) and extended X-ray absorption fine structure spectroscopy (EXAFS). These data revealed that Na ⁺ ions inside MXene galleries were exchanged by Eu ³⁺ ions and Eu(III) existed dominately in under outer-sphere surface complexation after adsorption under acidic pH conditions, but in inner-sphere surface complexation under near-neutral pH conditions. Due to its cost-effective prepatation and excellent sorption performance, Na-Ti₃C₂T_x may be a promising candidate for the efficient removal of trivalent minor actinides and lanthanides from radioactive wastewater.

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.

With the fast advancement of human modernization and rapid development of social economy, traditional energy consumption has been enormously increased and climate change has therefore become a very challenging issue for the human being. The development of modern industry, especially the chemical industry, has brought not only convenience to people, but also unprecedented destruction to the ecological environment closely related to human life. Energy and environmental issues have become a global challenge for us today. In order to better deal with the challenges and protect our living homeland, the majority of researchers are constantly seeking and exploring new materials and technologies which are environmentally friendly and can be used efficiently, aiming to solve increasingly serious environmental problems. In current stage, environmental materials and technologies have received ever-increasing attention and are developing rapidly.

Environmental materials, as the name implies, are materials designed and developed for environmental issues. The key issue of environmental problems is environmental pollution. At present, the widely concerned pollutants include gas pollutants, persistent organic pollutants (POPs), and heavy metals. At the same time, with drastic development of nuclear energy industry in the past two decades in China, radioactive pollutants have also received increasing attention. Separation and removal of these pollutants from environment by certain means is an effective and common method for environmental pollution control. Therefore, the key for solving environmental problems is to develop materials and technologies that can effectively remove environmental pollutants. Plenty of versatile materials for specific contaminant removals have been reported over the past few decades. These materials come in a wide variety of functions, with varying structures and performance. Most concerned materials include traditional molecular sieves^[1], mineral materials^[2], carbon materials such as graphene and carbon nanotubes^[3], polymer based materials such as resins^[4], metal organic frameworks (MOFs)^[5] and covalent organic frameworks (COFs)^[6]. Among these materials, inorganic materials have broad application prospects in the removal and separation of environmental pollutants due to their stability, low cost and environmental friendliness. In particular, inorganic nanoporous materials have become favorable in recent years. The nanometer size makes nanomaterials not only have quantum size effect, but also possess larger specific surface area and more surface atoms compared to other common materials, thus exhibiting stronger adsorption ability and better dispersibility in aqueous solution. In addition, the porosity of materials greatly enhances the specific surface area and correspondingly increases the contact opportunity between the material and contaminant. Meanwhile, it also improves the diffusion and transportation of contaminants inside the material, elevating the adsorption kinetics. Metal nanomaterials, metal oxide nanomaterials, mineral materials, etc. are typical representatives of inorganic nanomaterial family.

Based on the published works, many efforts in the field of inorganic environmental materials focused on improving the removal efficiency and selectivity toward one or more target pollutants. Inorganic materials have higher stability than organic materials, but possess low removal capacity and poor selectivity, due to lacking of active functional groups on the surface. Functionalization of inorganic materials should be a reasonable approach to overcome this drawback. It is well known that functional groups with strong binding or coordination ability to the target contaminant decorated on the surface of material by physical or chemical means can greatly improve the adsorption performance of inorganic materials^[7]. Moreover, besides modifying the specific recognition group on the surface of the material^[8], adjusting the pore structure of material and physically screening contaminants by the size effect^[9] are always common and effective. It is also promising to combine size effects, bonding and electrostatic interactions by means of molecular imprinting or composition^[10]. Besides, developing inorganic environmental materials used under harsh conditions^[11], such as high acid, high alkali, and high temperature, is becoming a research hot topic in recent years.

In all, after decades of development, researches on inorganic environmental materials have made significant progress, whereas most of materials are still not satisfactory for industrial applications. In order to better solve the increasingly serious environmental problems, it is still necessary for the material researchers to overcome difficulties and make continuous efforts.