Recent Advancements in Pyrolysis of Halogen-Containing Plastics for Resource Recovery and Halogen Upcycling: A State-of-the-Art Review.

Plastic waste has emerged as a serious issue due to its impact on environmental degradation and resource scarcity. Plastic recycling, especially of halogen-containing plastics, presents challenges due to potential secondary pollution and lower-value implementations. Chemical recycling via pyrolysis is the most versatile and robust approach for combating plastic waste. In this Review, we present recent advancements in halogen-plastic pyrolysis for resource utilization and the potential pathways from "reducing to recycling to upcycling" halogens. We emphasize the advanced management of halogen-plastics through copyrolysis with solid wastes (waste polymers, biomass, coal, etc.), which is an efficient method for dealing with mixed wastes to obtain high-value products while reducing undesirable substances. Innovations in catalyst design and reaction configurations for catalytic pyrolysis are comprehensively evaluated. In particular, a tandem catalysis system is a promising route for halogen removal and selective conversion of targeted products. Furthermore, we propose novel insights regarding the utilization and upcycling of halogens from halogen-plastics. This includes the preparation of halogen-based sorbents for elemental mercury removal, the halogenation-vaporization process for metal recovery, and the development of halogen-doped functional materials for new materials and energy applications. The reutilization of halogens facilitates the upcycling of halogen-plastics, but many efforts are needed for mutually beneficial outcomes. Overall, future investigations in the development of copyrolysis and catalyst-driven technologies for upcycling halogen-plastics are highlighted.

Unraveling the effect of particle size of active metals in Ni/MgO on methane activation and carbon growth mechanism.

For dry reforming of methane, the active metal particle size of the catalyst has a significant effect on both the reaction activity and the resistance to carbon deposition. In this study, nickel particles of different sizes (Ni13, Ni25, and Ni37) supported on the MgO(100) slab are used to study the mechanism of CH4 activation and carbon growth based on DFT theoretical calculations. According to the results, the energy of adsorption for reaction intermediates changes depending on the size of the active metal. The adsorption process of CH3, CH2, CH and C on Ni25/MgO has a maximum exothermic value. Furthermore, the energy barriers of CH4 four-step dehydrogenation are lowest on Ni25/MgO during the CH4 activation process. The growth process of carbon deposition on the catalysts is also investigated in this work. The results indicate that the growth of carbon from C5 to C6 is difficult to proceed on Ni13/MgO due to size and active site limitation. Additionally, with an increase in particle size of the active metal, the absolute value of growth energy and average carbon binding energy of Cn increase on both Ni25/MgO and Ni37/MgO. It is proved that smaller particle size presents better resistance to carbon deposition. In the studied size range, Ni25/MgO is demonstrated to have greater catalytic activity and better resistance to carbon deposition.

Effects of Cu ratios on the C1-C6 growth mechanism on copper-nickel bimetallic surfaces.

The adsorption and growth mechanisms of Cn (n = 1-6) on different Cu-Ni surfaces are calculated by density functional theory (DFT). The results demonstrate that Cu doping affects the growth mechanism of the deposited carbon on the catalyst surface. Firstly, the addition of Cu weakens the interaction between Cn and the adsorbed surface, which is proved by the results of density of states (DOS) and partial density of states (PDOS). The weakening of the interaction allows Cn to perform at higher proportions of Cu-doped surfaces with a behavior consistent with that in the gas phase. A comparison of the growth energies of the different pathways of Cn in the gas phase shows that the main pathway for the Cn growth is chain-to-chain (CC). The CC reaction is also the main pathway for the growth of Cn on the surfaces, which is enhanced by the doping of Cu. In addition, analysis of the growth energy revealed that C2-C3 is the rate-determining step in the growth process of Cn. The doping of Cu enhances the growth energy of this step, contributing to the suppression of the growth of the deposited carbon on the adsorbed surface. Moreover, an average carbon binding energy shows that the doping of Cu on the Ni surface could weaken the structural stability of Cn, favoring the elimination of carbon deposited on the catalyst surface.

Density Functional Theory Studies on the Hydrolysis of Levoglucosenone to 5-Hydroxymethylfurfural.

Selective conversion of lignocellulosic biomass-derived chemicals is of critical significance for sustainable fine and commodity chemical industries. Cellulose-derived levoglucosenone (LGO) has a promising potential for producing 5-hydroxymethylfurfural (HMF) with a substantial yield under acid conditions, but the mechanism is unidentified. Herein, we disclose the mechanism of LGO conversion to HMF in the aqueous phase without and with H2SO4 as a catalyst by density functional theory (DFT) calculations for the first time. Results showed that LGO first forms 6,8-dioxabicyclo[3.2.1]-octane-2,4,4-triol (DH) via two sequential hydration reactions occurring at the C═C bond and then the ketone group. The use of H2SO4 as a catalyst significantly reduced the free energy barriers of LGO and DH conversion to HMF, with a free energy barrier of 115 kJ/mol for LGO → HMF compared to that of 91 kJ/mol for DH → HMF, demonstrating that DH is easier for HMF formation.

From Spent Lithium-Ion Batteries to Low-Cost Li4SiO4 Sorbent for CO2 Capture.

The huge consumption of fossil fuels leads to excessive CO2 emissions, and its reduction has become an urgent worldwide concern. The combination of renewable energies with battery energy storage, and carbon capture, utilization, and storage are well acknowledged as two major paths in achieving carbon neutrality. However, the former route faces the discard problem of a large amount of lithium-ion batteries (LIBs) due to their limited lifespan, while it is costly to obtain effective CO2-capturing materials to put the latter into implementation. Herein, for the first time, we propose a route to synthesize low-cost Li4SiO4 as CO2 sorbents from spent LIBs, verify the technical feasibility, and evaluate the CO2 adsorption/desorption performance. The results show that Li4SiO4 synthesized from the cathode with self-reduction by the anode graphite of LIBs has a superior CO2 capacity and cyclic stability, which is constant at around 0.19 g/g under 15 vol % CO2 after 80 cycles. Moreover, the cost of fabricating sorbents from LIBs is only 1/20-1/3 of the conventional methods. We think this work can not only promote the recycling of spent LIBs but also greatly reduce the cost of preparing Li4SiO4 sorbents, and thus could be of great significance for the development of CO2 adsorption.

Continuous, Large-Scale, and High Proportion of Bioinspired Phosphogypsum Composites via Reactive Extrusion.

Biological matter evolution provides an idea for the human design and synthesis of new materials. However, biomimetic materials only stay in laboratory-scale models, and their large-scale industrial applications are yet to be realized. Here, inspired by nacre's architecture, we report a continuous, large-scale method to fabricate phosphogypsum composites by reactive extrusion strategy. After curing for seven days, with more than 50 wt% of beta-hemihydrate phosphogypsum (ß-HPG), the compressive strength and softening coefficient were 24.98 MPa and 0.78, increasing by 110.0% and 20.0%, respectively, compared to the pouring method. The results show that the screw extrusion process can improve the mechanical strength and waterproof properties of ß-HPG hydration specimens without any special chemical admixtures and cements.

Understanding the nature of NH3-coordinated active sites and the complete reaction schemes for NH3-SCR using Cu-SAPO-34 catalysts.

Cu-SAPO-34 zeolite catalysts show excellent NH3-SCR performance at low temperature, which is due to the catalytic capacity of copper species. Isolated CuII ions and CuIIOH are active sites, but their nature and role are not fully understood. This paper reports the DFT calculations in combination with ab initio thermodynamics to investigate NH3 and H2O coordination to copper species under typical NH3-SCR reaction conditions. In the reduction part of the NH3-SCR reaction, NH2NO and NH4NO2 intermediates will form on CuII-2NH3/3NH3 and CuIIOH-2NH3 complexes, respectively. The Brønsted acid sites are crucial for the decomposition of these intermediates, rather than copper species. Furthermore, the decomposition of NH2NO is more energetically favorable than NH4NO2 which are formed on the Brønsted acid sites. In the re-oxidation part of the NH3-SCR reaction, O2 dissociation and NO2 formation occur on CuI-2NH3 complexes in the presence of NO, and the regeneration of CuIIOH-2NH3 requires the participation of H2O. The proposed complete mechanisms highlight the importance of ligand coordinated copper species for intermediate formation and O2 activation in NH3-SCR.

Experimental and thermodynamic study of banana peel non-catalytic gasification characteristics.

The Gasification performance of banana peel was examined in a fixed bed reactor. Effect of temperature, steam to carbon ratio (S/C), drying treatment on syngas composition, gas yield, CO2 selectivity and carbon conversion efficiency (CCE) were investigated. The influence of temperature and S/C on hydrogen production was investigated by thermodynamic analysis. The transient characteristics of banana peel steam gasification were investigated by monitoring the evolutionary behavior of syngas production. An increase in S/C can lead to an increase in the selectivity of CO2, but excess steam (S/C > 21.7) causes a decrease in H2 yield and CCE. The increase of temperature is beneficial to the increase of CCE, but which leads to a decrease in CO2 selectivity. When S/C = 27.1, the effect of temperature on H2 yield can be divided into CCE control region and CO2 selectivity control region. At temperature < 1023 K, H2 yield is more sensitive to the changes of CCE. While at temperature > 1023 K, CO2 selectivity has a more significant effect on H2 yield. When S/C = 21.7 and temperature is 1023 K, the yield of H2 produced from the fresh banana peel gasification reaches the maximum value (76.1 ml/g).

Insight into the effect of facet-dependent surface and oxygen vacancies of CeO2 for Hg removal: From theoretical and experimental studies.

The reaction mechanisms of Hg oxidation on CeO2(111) and (110) surface are clarified by a group of designed experiments and density functional theory (DFT) calculations. CeO2 nanorods and nanoparticles with exposure (110) and (111) faces were prepared by hydrothermal methods, and their morphological properties were investigated using XRD, XPS and HRTEM. Combined experimental and DFT results, the nanorods show better activity than nanoparticles. The total oxidation of Hg can be partially prohibited by the high barriers for the incorporated chlorine activation at reduced surfaces, due to the strong electronic repulsion of heavily accumulated charges. The energy barrier profiles suggest Hg oxidation is much more favorable on CeO2(110) surface than that on CeO2(111) surface. In the Hg oxidation via HCl and O2, the role of O2 is not only replenishment of lattice oxygen, but also could generate surface oxygen as active center for HCl active. The complete catalytic cycle can be identified as four parts: (i) HCl activated by lattice oxygen, (ii) Hg oxidation on defect surface, (iii) HCl activated by adsorbed oxygen and (iv) Hg oxidation on stoichiometric surface. The results of this study provide deep insights into the effects of CeO2 nanocatalyst morphology on the Hg oxidation.

Irregular influence of alkali metals on Cu-SAPO-34 catalyst for selective catalytic reduction of NOx with ammonia.

SCR activity of Cu-SAPO-34 catalyst was reduced by alkali metal ions. The alkali metals ions (Li+, Na+ and K+) have shown irregular influences on Cu-SAPO-34. The order of poisoning strengths under 400 °C was found to be: Na+ > K+ > Li+, which is not consistent with the basicities of their corresponding metals. Experimental results and calculations showed that the alkali metal ions readily replace H+ and Cu2+/Cu+ ions. These exchanges result in the loss of Brønsted acid sites and migration of isolated Cu2+ ions in Cu-SAPO-34, which decrease the NH3-SCR activity. Both the basicity and ion diameter will affect the exchanging behavior of an alkali ion. Na+ and Li+ ions will influence both H+ and Cu2+/Cu+ ions but K+ ions only preferably replace the H+. We hypothesize that K+ cannot enter into a small ring (6-membered ring) to replace a Cu2+/Cu+ ion because of its large ion diameter. The displaced Cu2+/Cu+ ions will transfer to adjacent unbonded Al site to form a CuAlO2 species.

ZIF-8@polyoxometalate derived Si-doped ZnWO4@ZnO nanocapsules with open-shaped structures for efficient visible light photocatalysis.

In this work, we report silicon doped ZnWO4@ZnO nanocapsules with open-shaped structures obtained by a facile encapsulation-calcination strategy derived from ZIF-8 and polyoxometalates. Owing to the unique structure and elemental composition, the as-prepared samples respond well to visible light irradiation for degradating Rhodamine B. The possible photocatalytic reaction mechanisms are presented based on density functional theory (DFT) calculations.

Correction: ZIF-8@polyoxometalate derived Si-doped ZnWO4@ZnO nanocapsules with open-shaped structures for efficient visible light photocatalysis.

Correction for 'ZIF-8@polyoxometalate derived Si-doped ZnWO4@ZnO nanocapsules with open-shaped structures for efficient visible light photocatalysis' by Jingyu Ran et al., Chem. Commun., 2018, DOI: .

Rapid Ferric Transformation by Reductive Dissolution of Schwertmannite for Highly Efficient Catalytic Degradation of Rhodamine B.

In this study, reductive dissolution of iron oxides was considered for the acceleration of the transformation from Fe(III) to Fe(II) to improve the degradation of rhodamine B (RhB) by potassium persulfate (PS) activation on schwertmannite. The addition of hydroxylamine (HA) showed an enhancement effect on the degradation at pH 3 and 5, but insignificant efficiency of the addition was obtained at pH 9. The surface reduction from Fe(III)-OH to Fe(II)-OH by HA was considered dominant for the acceleration of PS activation through the reductive dissolution process, and the hydroxyl and sulfate radicals generated by the decomposition of surface complexes were main primary reactive oxidants that contributed to the degradation of RhB.

New Insight into Polydopamine@ZIF-8 Nanohybrids: A Zinc-Releasing Container for Potential Anticancer Activity.

Despite the initial evidence on the role of zinc and zinc transporters in cancer prevention, little attention has been paid to the zinc-derived compounds. In the present work, we reported a strategy to prepare a kind of zinc-releasing container with enhanced biocompatibility and release dynamics using ZIF-8 nanocrystals as the sacrificial templates. Transmission electron microscopy (TEM) analysis demonstrated that the ZIF-8 nanocrystals were gradually etched out in the aqueous media within 48 h, resulting in hollow nanocapsules. Notably, we found the self-polymerization of dopamine can form nanoshells around the ZIF-8 nanocrystals, which served as a type of functional membranes during the release of zinc. More interestingly, PDA@ZIF-8⁻based nanohybrids expressed stronger inhibition to the cancer cell growth, which implied that the nanohybrids could be a drug carrier for chemotherapy. This study broadens the biomedical application of ZIF-8 and also provides a versatile strategy toward the development of multifunctional delivery system.

Zeolitic imidazolate framework-8 (ZIF-8) as a sacrificial template: one-pot synthesis of hollow poly(dopamine) nanocapsules and yolk-structured poly(dopamine) nanocomposites.

Hollow poly(dopamine) (PDA) nanocapsules and yolk-structured PDA nanocomposites were prepared by an aqueous one-pot synthesis method utilizing zeolitic imidazolate framework-8 (ZIF-8) nanocrystals as a sacrificial template without any special etchant. The resulting PDA nanocapsules show negligible cytotoxicity in HeLa cells after incubation for 48 h at various doses, which implies their potential as candidates for practical applications in drug transport and targeting.

A facile method for improving the covalent crosslinking adsorption process of catalase immobilization.

In this paper, we introduced a polydiol (mixture of 1,2-propanediol, 1,3-propanediol, and 2,3-butanediol) to improve the covalent crosslinking adsorption process of immobilized catalase onto chitosan beads. The adsorption behavior was investigated by means of adsorption kinetics and adsorption isotherm. The protein content in crosslinking agent required for approximately 45 min to reach the relative equilibrium, and the protein content in solution of the control group and the pretreated group were 6.63 microg/mL and 6.20 microg/mL, respectively. The maximum catalase adsorption capacity of the control group and the pretreated group were observed as 23.118 microg/g and 25.688 microg/g at pH 7.0, respectively. Temperature profiles showed that 40 degrees C was the ideal temperature for active domain of catalase, and the relative activity of pretreated group was 1.12 times higher than that of the control group. The K(m) value of the control group (67 mM) was higher than that of the pretreated group (54 mM). Thermal stability, operational stability, and the effect of surfactant on catalase adsorption were also explored in this study.