Rapid iodine capture from radioactive wastewater by green and low-cost biomass waste derived porous silicon–carbon composite

Reusable cellulose-based biosorbents for efficient iodine adsorption by economic microcrystalline cellulose production from walnut shell

Sustainable management of walnut shell (WS) for the extraction of cellulose and preparation of cellulose-based biosorbents of iodine was carried out as a new approach to simultaneously solve the environmental challenge of agricultural solid waste and iodine-contaminated water. A rapid recyclable nitric acid treatment and NaOH-H2O2 alkaline-peroxide treatment of WS (33 % cellulose) extracted pure microcrystalline (Cac) and impure cellulose (Cal) with a 21.70 % and 47.37 % isolation yield, respectively. The techno-economic assessment of cellulose production showed a net profit of 9.02 $/kg for Cac, whereas it was estimated as negative for Cal. The simultaneous carbonization and magnetization of Cac at 550 °C resulted in an amorphous, magnetic cellulose-derived biochar (MB550Cac) with a BET specific surface area of 12.64 m2/g, decorated with scattered irregular Fe3O4 microparticles. The adsorption capacity of MB550Cac for iodine was 555.63 mg/g, which was lost only 17.45 % after six successful cycles of regeneration. Freundlich isotherm model sufficiently described the reversible iodine adsorption on the heterogenous surface. The adsorption kinetics followed the pseudo-second-order model. Further, the adsorption thermodynamics demonstrated spontaneous and favorable adsorption. These findings suggest the valorization of WS to commercially produce cellulose and MB550Cac as a sustainable, efficient biosorbent with a good application prospect in wastewater treatment.

Dynamic and transformable Cu12 cluster-based C-H···π-stacked porous supramolecular frameworks

The assembly of cluster-based π-stacked porous supramolecular frameworks presents daunting challenges, including the design of suitable cluster building units, control of the sufficient C-H···π interactions, trade-off between structural dynamics and stability as well as understanding the resulting collective properties. Herein, we report a cluster-based C-H···π interaction-stacked porous supramolecular framework, namely, Cu12a-π, consisting of Cu12 nanocluster as a 6-connected node, which is further propagated to a dynamic porous supramolecular frameworks via dense intralayer C-H···π interactions, yielding permanent porosity. In addition, Cu12a-π can be transformed into cluster-based nonporous adaptive crystals (Cu12b-NACs) via ligand-exchange following a dissociation-reassembly mechanism. Moreover, Cu12a-π can efficiently remove 97.2% of iodine from saturated iodine aqueous solutions with a high uptake capacity of 2.96 g·g-1. These prospective results positioned at cluster-based porous supramolecular framework and enlighten follow-up researchers to design and synthesize such materials with better performance.

In Situ Confined Synthesis of a Copper-Encapsulated Silicalite-1 Zeolite for Highly Efficient Iodine Capture

Effective capture of radioactive iodine is highly desirable for decontamination purposes in spent fuel reprocessing. Cu-based adsorbents with a low cost and high chemical affinity for I2 molecules act as a decent candidate for iodine elimination, but the low utilization and stability remain a significant challenge. Herein, a facile in situ confined synthesis strategy is developed to design and synthesize a copper-encapsulated flaky silicalite-1 (Cu@FSL-1) zeolite with a thickness of ≤300 nm. The maximum iodine uptake capacity of Cu@FSL-1 can reach 625 mg g-1 within 45 min, which is 2 times higher than that of a commercial silver-exchanged zeolite even after nitric acid and NOX treatment. The Cu nanoparticles (NPs) confined within the zeolite exert superior iodine adsorption and immobilization properties as well as high stability and fast adsorption kinetics endowed by the all-silica zeolite matrix. This study provides new insight into the design and controlled synthesis of zeolite-confined metal adsorbents for efficient iodine capture from gaseous radioactive streams.

Legal Guarantee of Smart City Pilot and Green and Low-Carbon Development

Green and smart cities are based on clean energy and rely on information technology. They are the guarantee for the realization of efficient and intelligent urban development and green ecological transformation, the basis for sustainable social and economic development, and the inevitable trend of urban development. Therefore, the evaluation of the development level of green and smart cities is of great significance to the development of Chinese cities. This paper has aimed to study the issue of smart city pilots and legal guarantees for green and low-carbon development and introduced the concept of smart city line management, as well as the related theory of entropy weight method, cloud model, and support vector machine algorithm. Based on the sustainable development index system, this paper has combined the low-carbon concept to construct the low-carbon city evaluation index system and carried out an empirical analysis. The sustainable development index system, the research results of low-carbon city, and the current situation and characteristics of low-carbon city construction are studied and analyzed. On this premise, a low-carbon city assessment framework in view of reasonable improvement is built, including low-carbon economy, low-carbon society, low-carbon climate, and low-carbon component. The experimental results of this paper show that the low-carbon environment subsystem has the best coordinated development among the four subsystems, and the current state is the best. By 2021, the coordination degree value has reached 0.6656, which is in a relatively coordinated state.

Synthesis of Iron(II) Clathrochelate-Based Poly(vinylene sulfide) with Tetraphenylbenzene Bridging Units and Their Selective Oxidation into Their Corresponding Poly(vinylene sulfone) Copolymers: Promising Materials for Iodine Capture

The development of a simple and efficient synthetic methodology to engineer functional polymer materials for gas adsorption is necessary due to its relevance for various applications. Herein, we report the synthesis of metalorganic poly(vinylene sulfide) copolymers CTP1-3 with iron(II) clathrochelate of various side groups connected by tetraphenylbenzene units. CTP1-3 were subsequently oxidized into their respective poly(vinylene sulfone) copolymers CTP4-6 under green reaction conditions. The target copolymers CTP1-6 were characterized using various instrumental analysis techniques. Examination of the iodine adsorption properties of the copolymers revealed high iodine uptake properties, reaching 2360 mg g−1 for CTP2, and whose reusability tests proved its efficient regeneration, thus proving the importance of iron(II) clathrochelate polymers in iodine capture.

Recent Advances in Carbon-Silica Composites: Preparation, Properties, and Applications

The thermal catalytic conversion of biomass is currently a prevalent method for producing activated carbon with superb textural properties and excellent adsorption performance. However, activated carbon suffers severely from its poor thermal stability, which can easily result in spontaneous burning. In contrast, silica material is famed for its easy accessibility, high specific surface area, and remarkable thermal stability; however, its broader applications are restricted by its strong hydrophilicity. Based on this, the present review summarizes the recent progress made in carbon-silica composite materials, including the various preparation methods using diverse carbon (including biomass resources) and silica precursors, their corresponding structure–function relationship, and their applications in adsorption, insulation, batteries, and sensors. Through their combination, the drawbacks of the individual materials are circumvented while their original advantages are maintained. Finally, several bottlenecks existing in the field of carbon-silica composites, from synthesis to applications, are discussed in this paper, and possible solutions are given accordingly.

Enhanced removal of radioactive iodine anions from wastewater using modified bentonite: Experimental and theoretical study

Efficient and cost-effective removal of radioactive iodine anions from contaminated water has become a crucial task and a great challenge for waste treatment and environmental remediation. Herein, we present hexadecylpyridinium chloride monohydrate modified bentonite (HDPy-bent) for the efficient and selective removal of iodine anions (I^- and IO₃^-) from contaminated water. Batch experiments showed that HDPy-bent could remove more than 95% of I^- and IO₃^- within 10 min, and had maximum I^- and IO₃^- adsorption capacities of 80.0 and 50.2 mg/g, respectively. Competitive experiments indicated that HDPy-bent exhibited excellent I^- and IO₃^- selectivity in the excessive presence of common concomitant anions including PO₄^3-, SO₄^2-, HCO₃^-, NO₃^-, Cl^- (maximum mole ratio of anions vs iodine anions was ∼50,000). An anion exchange mechanism was proposed for the selective adsorption of iodine anions. Optimal adsorption structure of HDPy⁺/I^- (IO₃^-) at atomic level and driving forces of the I^- (IO₃^-) adsorption were calculated by density functional theory (DFT) simulations. Moreover, the good durability and reusability of the HDPy-bent has been demonstrated with 5 adsorption-desorption cycles. Dynamic column experiment also demonstrated that HDPy-bent exhibited excellent removal and fractional recovery capabilities towards I^- and IO₃^- from simulated groundwater and environmental water samples. In conclusion, this work presents a promising adsorbent material for the decontamination of radioactive iodine anions from wastewater on a large scale.

Preparation and characterization of three-dimensional hierarchical porous carbon from low-rank coal by hydrothermal carbonization for efficient iodine removal

Low-rank coal, such as Shengli lignite (SL) and Datong bitumite (DT), has abundant reserves and is low in cost. Due to its high moisture content, abundant oxygen-containing groups, high ash content and low calorific value, low-rank coal is mainly used in a low-cost method of direct combustion. For better value-added utilization of SL and DT, a novel strategy has been developed for the preparation of oxygen-rich hierarchical porous carbons (HPCs) by hydrothermal carbonization (HTC), followed by steam activation. In this paper, firstly, the physical and chemical properties of SL and DT were improved by HTC pretreatment, bringing them closer to high rank coal. Then, the effects of HTC pretreatment and activation temperature on the properties of the HPCs were investigated in detail. The results show that the HPCs have mainly microporous structures (the microporosity of 200-SLHPC-900 is 79.58%) based on the N2 adsorption-desorption isotherm analysis and exhibit a higher specific surface area (SSA) and larger pore volume (25.02% and 2.69% improvement for 200-SLHPC-900; 4.93% and 14.25% increase for 200-DTHPC-900, respectively) after HTC pretreatment. The two types of HPCs also present good adsorption performance. The iodine adsorption value of lignite-based HPC presents an increase of 13.72% from 503 mg g-1 to 572 mg g-1, while the value of bitumite-based HPC increases up to 924 mg g-1. A preliminary additional HTC step is therefore an effective method by which to promote the performance of low-rank coal based porous carbon. The process of hydrothermal carbonization and steam activation is a cost-effective and environmentally-friendly preparation method, which omits the use of a chemical activator and reduces the step of alkaline waste liquid discharge compared with the route of carbonization and chemical activation.

Calix[4]pyrrole-based Crosslinked Polymer Networks for Highly Effective Iodine Adsorption from Water

A series of calix[4]pyrrole-based crosslinked polymer networks designed for iodine capture is reported. These materials were prepared by Sonogashira coupling of α,α,α,α-tetra(4-alkynylphenyl)calix[4]pyrrole with bishalide building blocks with different electronic properties and molecular sizes. Despite their low Brunauer-Emmett-Teller surface areas, iodine vapor adsorption capacities of up to 3.38 g g^-1 were seen, a finding ascribed to the presence of a large number of effective sorption sites including macrocyclic π-rich cavities, aryl units, and alkyne groups within the material. One particular system, C[4]P-BTP, was found to be highly effective at iodine capture from water (uptake capacity of 3.24 g g^-1 from a concentrated aqueous KI/I₂ solution at ambient temperature). Fast capture kinetics (k_obs =7.814 g g^-1  min^-1 ) were seen. Flow-through adsorption experiments revealed that C[4]P-BTP is able to remove 93.2 % of iodine from an aqueous source phase at a flow rate of 1 mL min^-1 .