Cage-Based Covalent Organic Framework for the Effective and Efficient Removal of Malachite Green from Wastewater.

A cage-covalent organic framework (COF)-TP {T = bis(tetraoxacalix[2]arene[2]triazine); P = piperazine}, a novel two-dimensional covalent organic skeleton substituted with a nucleophilic cyanuric chloride analogue, was synthesized by a simple polymerization process. Cage-COF-TP is advantageous owing to its good structural order, permanent porosity, and low preparation cost. This skeleton was employed as a cost-effective adsorbent for the intermittent adsorption of an organic dye from aqueous solutions. Adsorption experiments were carried out at different initial dye concentrations, contact times, and solution pH. The adsorption kinetics followed the pseudo-second order model, and the results of thermodynamic studies were consistent with the Langmuir isotherm model. The high degree of matching between the size and shape of malachite green (MG) and the shrunken channels present in Cage-COF-TP were responsible for the enhanced adsorption ability of this material. Furthermore, theoretical calculations indicated that the high adsorption of the studied adsorbent can be attributed to the presence of nitrogen-rich triazine units in the Cage-COF-TP, which are expected to strengthen its affinity to guest molecules. The obtained results showed that the developed adsorbent is an efficient adsorbent that is theoretically capable of stimulating the removal of ∼2000 mg/g MG from wastewater at ambient temperature. This study will therefore be expected to promote the development of new functional materials based on COFs.

2D graphene/FeOCl heterojunctions with enhanced tribology performance as a lubricant additive for liquid paraffin.

The purpose of this study is to prepare graphene/FeOCl (G/FeOCl) heterojunctions via a microwave-pyrolysis approach and probe into the synergistic lubrication of G with FeOCl in liquid paraffin (LP). The morphology and chemical composition of specimens were analysed by utilizing scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and X-ray photoelectron spectroscopy (XPS) techniques. The tribological property of G/FeOCl was determined, and the interaction between the G/FeOCl heterojunction and friction pair was carried out through simulation calculations. The results indicated that neither G nor FeOCl significantly improved the lubrication performance of LP. However, together with FeOCl, G as lubrication additives greatly improved the lubrication performance of LP. Under the load of 1.648 GPa, the mean friction coefficient and wear scar diameter of LP containing 0.20 wt% G/FeOCl were 66.1% and 44.7% inferior to those of pure LP, respectively. Scanning electron microscopy (SEM) and elemental mapping analyses of worn scars revealed the formation of G/FeOCl layer tribofilms that prevent direct contact between metals. In addition, the high interfacial energy between graphene and FeOCl calculated based on first-principles density functional theory (DFT) further confirmed that graphene and FeOCl simultaneously form friction films with wear resistance and wear reduction effect at the friction interface, which is consistent with the experimental results. This study, therefore, provides a pathway for low-friction lubricants by deploying G/FeOCl two-dimensional material systems.

Crucial roles of graphene oxide in preparing alginate/nanofibrillated cellulose double network composites hydrogels.

In this study, a novel strategy to prepare sodium alginate (SA)/nano fibrillated cellulose (NFC) double network (DN) hydrogel beads with the aid of graphene oxide (GO) was developed. In comparison with the multi-step freezing-thawing method, this study employs a facile one-step freeze drying method with the presence of GO sheets. The crucial roles of GO were highlighted as an efficient nucleating agent of NFC and a reinforcer for the hydrogel. The adsorption property of the DN hydrogel towards crystal violet (CV) was also studied. Results indicated that the introduction of GO could greatly facilitate the formation of double networks. Furthermore, the as-prepared DN hydrogel beads exhibited an efficacious adsorption property towards CV. The maximum adsorption capacity of the hydrogels for CV was observed as 665 mg g-1. Therefore, our approach here represents a facile method for the preparation of crystalline polymer based DN hydrogels to replace the awkward freezing-thawing process, giving inspiration for DN hydrogels design and preparation. Moreover, due to its efficient adsorption capacity, the hydrogels hold great promise for the water pollution control materials.

Partly reduced graphene oxide aerogels induced by proanthocyanidins for efficient dye removal.

In this study, a novel surface modified and partly reduced graphene oxide (PRGO) induced by mild oligomeric proanthocyanidins (OPC) was prepared for efficient dye removal. The in situ partial reduction, modification and assembly of GO sheets into OPC-PRGO aerogels were readily realized by a hydrothermal process. Systemically characterizations were performed to confirm the partial reduction and modification of GO by OPC. The OPC-PRGO aerogels exhibited a honeycomb-like structure rather than a snowflake-like structure of GO aerogel. Due to its unique structure, the OPC-PRGO aerogels exhibited an excellent adsorption property towards organic dyes, such as methylene blue (MB), neutral red (NR), amino black (AB) and Congo red (CR). The removal efficiencies of OPC-PRGO towards MB, NR, AB and CR were observed to be 97.5, 94.5, 87.2 and 88.2%, respectively. This study opens a new insight for understanding and preparing partly reduced GO instead of completely reduced GO for hydrophilic polymer/graphene composites.

Graphene Oxide Reinforced Alginate/PVA Double Network Hydrogels for Efficient Dye Removal.

Dually crosslinked graphene oxide reinforced alginate/polyvinyl alcohol (PVA) double network (DN) hydrogels were prepared via a facile freeze/thaw method followed by soaking in a Ca2+ solution. The morphology and structure of the hydrogels were systematically examined by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). The effects of pH, dosage of hydrogel, adsorption time, and temperature on the adsorptive property of DN hydrogels towards methylene blue (MB) were also studied. Results indicated that the hydrogels exhibited typical 3D porous structures and had an efficient adsorption effect towards MB due to strong interactions between DN hydrogels and MB molecules. The adsorption isotherm was found to coincide with the Langmuir model with a monolayer adsorption. The highest adsorption capacity of DN hydrogels for MB was examined as 480.76 mg·g-1.

Broadband near-infrared quantum cutting by Ce-Yb codoped YAG transparent glass ceramics for silicon solar cells.

Ce3+-Yb3+ co-doped transparent glass ceramics containing YAG nanocrystals were prepared by a conventional melt-quenching method. Broadband near infrared quantum cutting was achieved in the glass ceramics and proved to be a cooperative down-conversion process. Under 460 nm excitation, 2F5/2 to 5d1 electronic transitions occurred in Ce3+ and transferred their energy to two neighboring Yb3+. The dependence of the luminescence spectra and decay curves on Yb3+ concentration was investigated to understand the energy transfer mechanism. The energy transfer efficiency and the down-conversion quantum efficiency were estimated to be as high as 77.8% and 177.8%, respectively. This work will open a new route towards increased efficiency in silicon solar cells.

Effect of polyethyleneimine modified graphene on the mechanical and water vapor barrier properties of methyl cellulose composite films.

A series of novel methyl cellulose (MC) composite films were prepared using polyethyleneimine reduced graphene oxide (PEI-RGO) as an effective filler for water vapor barrier application. The as-prepared PEI-RGO/MC composites were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, tensile test and scanning electron microscopy. The experimental and theoretical results exhibited that PEI-RGO was uniformly dispersed in the MC matrix without aggregation and formed an aligned dispersion. The addition of PEI-RGO resulted in an enhanced surface hydrophobicity and a tortuous diffusion pathway for water molecules. Water vapor permeability of PEI-RGO/MC with loading of 3.0% of surface modified graphene was as low as 5.98×10-11gmm-2s-1Pa-1. The synergistic effects of enhanced surface hydrophobicity and tortuous diffusion pathway were accounted for the improved water vapor barrier performance of the PEI-RGO/MC composite films.

Broadband ultraviolet to near infrared conversion in Eu2+,Nd3+ co-doped SrAl2O4.

In this study, we investigated the quantum cutting (QC) mechanism in Eu2+-Nd3-co-doped SrAl2O4 microcrystals by fluorescence spectroscopy and decay lifetime analysis. In this material, the near-infrared (NIR) emissions of Nd3+ in the range of 800-1200 nm were enhanced under the excitation of the Eu2+:4f7 → 4f65d1 transition radiation. The lifetime of the 5d1 level of Eu2+ decreased with the increase in the Nd3+ concentration. These results verified the occurrence of cooperative energy transfer (CET) from the Eu2+:5d1 excited state to the Nd3+:4F3/2 level, by which one absorbed ultraviolet-visible photon was converted to two NIR photons with an optimal quantum efficiency (QE) of approximately 177.1%. Therefore, this broadband QC material paves the way for a further increase in the conversion efficiency of c-Si solar cells.