Low-cost eggshell-fly ash adsorbent for phosphate recovery: A potential slow-release phosphate fertilizer.

Fly ash (FA) and eggshells (ES) are common solid wastes with significant potential for the recovery of phosphorus from water. This study focuses on synthesizing a low-cost and environmental-friendly phosphate adsorbent called eggshell-fly ash geopolymer composite (EFG) using eggshells instead of chemicals. The CaO obtained from the high-temperature pyrolysis of eggshells provides active sites for phosphate adsorption, and CO2 serves as a pore-forming agent. The phosphate adsorption performance of EFG varied with the eggshell-fly ash ratios and achieved a maximum of 49.92 mg P/g at an eggshell-fly ash ratio of 40 %. The adsorption process was well described by the pseudo-second-order model and the Langmuir model. EFG also exhibited a good regeneration performance through six-cycle experiments and achieved the highest phosphate desorption at pH 4.0. The results of the column experiment showed that EFG can be used as a filter media for phosphorus removal in a real-scale application with low cost. Soil burial test indicated saturated EFG has a good phosphate slow-release performance (maintained for up to 60 days). Overall, EFG has demonstrated to be a promising adsorbent for phosphorus recovery.

Selective transformation and removal of As(III) by constructed Fe-N bonds: The generation of singlet oxygen from the photoexcitation of MnPc leads to abundant ZnFe-LDH interface OH radical.

In this study, MnPc intercalated Zn/Fe layered double hydroxides (MnPc/ZF-LDH) were synthesized by pillared intercalation modification with different MnPc intercalation amounts and used for the selective transformation and removal of As(III) from the arsenate-phosphate mixed solution. Fe-N bonds were constructed by the complexation of MnPc and iron ions on the Zn/Fe layered double hydroxides (ZF-LDH) interface. The DFT calculation results show that the binding energy of Fe-N bonded to arsenite (-3.75 eV) was higher than that of phosphate (-3.16 eV), resulting in MnPc/ZnFe-LDH exhibiting high As(III) selective adsorption performance and anchoring it rapidly in the arsenite -phosphate mixed solution. The maximum adsorption capacity of 1MnPc/ZF-LDH for As(III) could reach 180.7 mg·g-1 under dark conditions. MnPc also acts as a photosensitizer to provide more active species for the photocatalytic reaction. A series of experiments demonstrated that MnPc/ZF-LDH exhibits high As(III) selective photocatalytic performance. A total of 10 mg·L-1 of As(III) was completely removed in the reaction system within 50 min in a single As(III) environment. In an environment with As(III) and PO43-, it achieved 80.0 % removal efficiency of As(III) and showed a good reuse effect. The introduction of MnPc could improve the utilization of visible light by the MnPc/ZnFe-LDH. The singlet oxygen generated from photoexciting MnPc leads to abundant ZnFe-LDH interface OH. In addition, MnPc/ZnFe-LDH shows good recyclability, making it a promising multifunctional material for the purification of arsenic-polluted sewage.

One-dimensional alignment of defects in a flexible metal-organic framework.

Crystalline materials are often considered to have rigid periodic lattices, while soft materials are associated with flexibility and nonperiodicity. The continuous evolution of metal-organic frameworks (MOFs) has erased the boundaries between these two distinct conceptions. Flexibility, disorder, and defects have been found to be abundant in MOF materials with imperfect crystallinity, and their intricate interplay is poorly understood because of the limited strategies for characterizing disordered structures. Here, we apply advanced nuclear magnetic resonance spectroscopy to elucidate the mesoscale structures in a defective MOF with a semicrystalline lattice. We show that engineered defects can tune the degree of lattice flexibility by combining both ordered and disordered compartments. The one-dimensional alignment of correlated defects is the key for the reversible topological transition. The unique matrix is featured with both rigid framework of nanoporosity and flexible linkage of high swellability.

Molecular identification and quantification of defect sites in metal-organic frameworks with NMR probe molecules.

The defects in metal-organic frameworks (MOFs) can dramatically alter their pore structure and chemical properties. However, it has been a great challenge to characterize the molecular structure of defects, especially when the defects are distributed irregularly in the lattice. In this work, we applied a characterization strategy based on solid-state nuclear magnetic resonance (NMR) to assess the chemistry of defects. This strategy takes advantage of the coordination-sensitive phosphorus probe molecules, e.g., trimethylphosphine (TMP) and trimethylphosphine oxide (TMPO), that can distinguish the subtle differences in the acidity of defects. A variety of local chemical environments have been identified in defective and ideal MOF lattices. The geometric dimension of defects can also be evaluated by using the homologs of probe molecules with different sizes. In addition, our method provides a reliable way to quantify the density of defect sites, which comes together with the molecular details of local pore environments. The comprehensive solid-state NMR strategy can be of great value for a better understanding of MOF structures and for guiding the design of MOFs with desired catalytic or adsorption properties.

Eggshell based biochar for highly efficient adsorption and recovery of phosphorus from aqueous solution: Kinetics, mechanism and potential as phosphorus fertilizer.

Development of an efficient and green adsorbent is of great significance for phosphorus removal and recovery from eutrophic water. This work prepared an eggshell modified biochar (ESBC) by co-pyrolysis of eggshells and corn stalk. ESBC exhibited an excellent performance for phosphorus adsorption over a wide pH range (5-13), and achieved a maximum adsorption of 557.0 mg P/g. The adsorption process was well fitted by pseudo-second-order model (R2 > 0.962) and Sips model (R2 > 0.965), and it was endothermic (ΔH0 > 0) and spontaneous (ΔG0 < 0) according to thermodynamic analysis. The column experiment confirmed the feasibility of ESBC as a filter media for phosphorus removal in flow condition, and obtained a P removal of 460.0 mg/g. Soil burial tests indicated P-laden ESBC has a good P slow-release performance (maintained for up to 25 days). Overall, ESBC has a promising application potential as an efficient adsorbent for phosphorus recovery and subsequently as a slow-release fertilizer.

Simultaneous oxidation of As(III) and reduction of Cr(VI) by NiS-CdS@biochar through efficient oxalate activation: The key role of enhanced generation of reactive oxygen species.

The reutilization of exhausted biochar is attracting extensive interest among researchers. In this study, the biochar generated from Chinese fir with natural regular porous structure that adsorbed Cd2+/Ni2+ at different concentration levels was used as the precursor, and then combined with simple hydrothermal vulcanization and ion deposition to generate the p-n heterojunction between NiS and CdS compounds (NiS-CdS@C) in situ. The hybrids with 3 cycles of NiS deposition reduced the interfacial transmission resistance from 80 Ω to 40 Ω, and increased photocurrent density by 5 times, thus effectively promoting the separation of photogenerated electrons and holes. The simultaneous removal of As(III) and Cr(VI) was selected to evaluate the oxidation and reduction capacity of the visible light/NiS-CdS@C/oxalate system. The results indicated that 10 mg/L As(III) and Cr(VI) were completely and simultaneously removed with 0.75 mM oxalate addition within 40 min in the system, and the NiS-CdS@C presented good durability and stability for oxalate activation. Electron paramagnetic resonance (EPR) and quenching experiments demonstrated that oxalate was activated by holes under light to produce •CO2- and enhanced the generation of additional •OH and •O2-, further contributing to the oxidation of As(III) and reduction of Cr(VI).

Defect-Assisted Loading and Docking Conformations of Pharmaceuticals in Metal-Organic Frameworks.

Understanding of drug-carrier interactions is essential for the design and application of metal-organic framework (MOF)-based drug-delivery systems, and such drug-carrier interactions can be fundamentally different for MOFs with or without defects. Herein, we reveal that the defects in MOFs play a key role in the loading of many pharmaceuticals with phosphate or phosphonate groups. The host-guest interaction is dominated by the Coulombic attraction between phosphate/phosphonate groups and defect sites, and it strongly enhances the loading capacity. For similar molecules without a phosphate/phosphonate group or for MOFs without defects, the loading capacity is greatly reduced. We employed solid-state NMR spectroscopy and molecular simulations to elucidate the drug-carrier interaction mechanisms. Through a synergistic combination of experimental and theoretical analyses, the docking conformations of pharmaceuticals at the defects were revealed.

In situ solid-state NMR characterization of pharmaceutical materials: An example of drug-polymer thermal mixing.

Pharmaceutical amorphous solid dispersions, a multicomponent system prepared by dispersing drug substances into polymeric matrix via thermal and mechanical processes, represent a major platform to deliver the poorly water-soluble drug. Microscopic properties of drug-polymer contacts play mechanistic roles in manipulating long-term physical stability as well as dissolution profiles. Although solid-state nuclear magnetic resonance has been utilized as an indispensable tool to probe structural details, previous studies are limited to ex situ characterizations. Our work provides likely the first documented example to investigate comelting of ketoconazole and polyacrylic acid, as a model system, in an in situ manner. Their physical mixture is melted and mixed in the solid-state nuclear magnetic resonance rotor under magic angle spinning at up to approximately 400 K. Critical structural events of molecular miscibility and interaction have been successfully identified. These results design and evaluate the instrumental and experimental protocols for real-time characterizations of the comelting of pharmaceutical materials.

Simple non-fused electron acceptors for efficient and stable organic solar cells.

The flexibility in structural design of organic semiconductors endows organic solar cells (OSCs) not only great function-tunabilities, but also high potential toward practical application. In this work, simple non-fused-ring electron acceptors are developed through two-step synthesis from single aromatic units for constructing efficient OSCs. With the assistance of non-covalent interactions, these rotatable non-fused acceptors (in solution) allow transiting into planar and stackable conformation in condensed solid, promoting acceptors not only feasible solution-processability, but also excellent film characteristics. As results, decent power conversion efficiencies of 10.27% and 13.97% can be achieved in single and tandem OSCs consisting of simple solution-cast blends, in which the fully unfused acceptors exhibit exceptionally low synthetic complexity index. In addition, the unfused acceptor and its based OSCs exhibit promising stabilities under continuous illumination. Overall, this work reveals valuable insights on the structural design of simple and effective electron acceptors with great practical perspectives.

Duet of Acetate and Water at the Defects of Metal-Organic Frameworks.

Metal-organic frameworks (MOFs) are porous crystalline materials with promising applications in molecular adsorption, separation, and catalysis. It has been discovered recently that structural defects introduced unintentionally or by design could have a significant impact on their properties. However, the exact chemical composition and structural evolution under different conditions at the defects are still under debate. In this study, we performed multidimensional solid-state nuclear magnetic resonance (SSNMR) coupled with computer simulations to elucidate an important scenario of MOF defects, uncovering the dynamic interplay between residual acetate and water. Acetate, as a defect modulator, and water, as a byproduct, are prevalent defect-associated species, which are among the key factors determining the reactivity and stability of defects. We discovered that acetate molecules coordinate to a single metal site monodentately and pair with water at the neighboring position. The acetates are highly flexible, which undergo fast libration as well as a slow kinetic exchange with water through dynamic hydrogen bonds. The dynamic processes under variable temperatures and different hydration levels have been quantitatively analyzed across a broad time scale from microseconds to seconds. The integration of SSNMR and computer simulations allows a precision probe into defective MOF structures with intrinsic dynamics and disorder.

Prevalence and outcomes of cataract surgery in rural China the China nine-province survey.

PURPOSE: To investigate the prevalence and visual acuity (VA) outcomes of cataract surgery in rural populations throughout China. DESIGN: Population-based, cross-sectional study. PARTICIPANTS: Forty-five thousand seven hundred forty-seven adults 50 years of age and older. METHODS: Geographically defined cluster sampling was used in randomly selecting a cross-section of residents from a representative rural county within each of 9 provinces in mainland China. Participants underwent VA measurements, refraction, and a slit-lamp examination at local examination sites; those with previous cataract surgery were queried as to the year and type of surgical facility. Surgical procedure and evidence of surgery complications were noted during the examination. The principal cause of visual impairment was identified for eyes with VA of 20/40 or worse. MAIN OUTCOME MEASURES: Cataract surgery procedure, presenting and best-corrected distance VA, and causes of visual impairment. RESULTS: Of 50 395 enumerated eligible persons, 45 747 (90.8%) were examined and tested for VA. The overall prevalence of cataract surgery was 2.09%. Surgical coverage among those with VA worse than 20/200 in both eyes because of cataract was 35.7%. Unoperated cataract was associated with older age, female gender, lack of education, and geographic area (province). Among the 1174 cataract-operated eyes, 31.1% had presenting VA of 20/32 or better, 15.4% had presenting VA of 20/40 to 20/63, 30.0% had presenting VA worse than 20/63 to 20/200, and 23.5% had presenting VA worse than 20/200. With best correction, the percentages were 57.6%, 6.2%, 18.5%, and 17.7%, respectively. Posterior capsule opacification, refractive error, and retinal disorders were the main causes in cataract-operated eyes with VA worse than 20/63. CONCLUSIONS: Two thirds of those with bilateral visual impairment or blindness because of cataract remain in need of sight-restoring surgery. Posterior capsule opacification and refractive error, both readily amenable to treatment, were common in cataract-operated eyes. Sustained government efforts to provide access to affordable modern cataract surgery with a greater emphasis on postoperative follow-up and the quality of VA outcomes are needed. FINANCIAL DISCLOSURE(S): The author(s) have no proprietary or commercial interest in any materials discussed in this article.

Prevalence of vision impairment in older adults in rural China: the China Nine-Province Survey.

PURPOSE: Describe the prevalence of visual impairment/blindness among older adults in rural populations in China. DESIGN: Population-based, cross-sectional study. PARTICIPANTS: We evaluated 45 747 adults > or =50 years of age. METHODS: Geographically defined cluster sampling was used in randomly selecting a cross-section of residents from a representative rural county within each of 9 provinces in mainland China. Participants were enumerated through village registers followed by door-to-door household visits. Eligible persons were invited to local examination sites for visual acuity (VA) testing and eye examination. MAIN OUTCOME MEASURES: Presenting and best-corrected distance VA. RESULTS: Of 50 395 enumerated eligible persons, 45 747 (90.8%) were examined and tested for VA. The prevalence of presenting visual impairment <20/63 to > or =20/400 in the better eye was 10.8% and blindness (<20/400) was 2.29%. Across the 9 provinces, presenting visual impairment ranged from 6.89% to 15.8%, and blindness from 1.27% to 5.40%. With best-corrected VA, the prevalence of visual impairment was 5.30%, and 1.93% for blindness. The ranges across the 9 provinces were 3.13% to 9.51% for visual impairment and 0.74% to 4.95% for blindness. Visual impairment and blindness were associated with older age, female gender, lack of education, and geographic area (province) with both presenting and best-corrected VA. CONCLUSIONS: Visual impairment and blindness are important public health problems in rural China, with significant regional variations in prevalence. Blindness prevention programs targeting the rural elderly should be expanded, particularly in areas with limited access and affordability of eye care services. Special emphasis should be given to reaching women and those without education. Greater attention should also be given to correction of refractive error.