Enabling white color tunability in complex 3D-printed composites by using lead-free self-trapped exciton 2D perovskite/carbon quantum dot inks.

The generation of stable white light emission using lead-free perovskites remains a huge challenge in the development of future display and lighting technologies, due to fast material deterioration and the decrease of the color quality. In this work, we report a combination of diverse types of 2D A2SnX4 (A = bulky cation, X = Br, I) perovskites exhibiting self-trapped exciton (STE) emission and blue luminescent carbon quantum dots (CQDs), with the purpose of generating A2SnX4/CQD inks with a broadband emission in the visible region and a tunable white light color. By varying the concentration of the 2D perovskite, the white emission of the mixtures is modulated to cool, neutral, and warm tonalities, with a PL quantum yield up to 45%. From the combinations, the PEA2SnI4/CQD-based ink shows the longest stability, due to suitable surface ligand passivation provided by the capping ligands covering the CQDs, compensating the defect sites in the perovskite. Then, by incorporating the PEA2SnI4/CQDs inks into an acrylate polymer matrix, the quenching of the PL component from the perovskite was restrained, being stable for >400 h under ambient conditions and at a relative humidity of ∼50%, and allowing the preparation of complex 3D-printed composites with stable white emission tonalities. This contribution offers an application of STE-based Sn-perovskites to facilitate the future fabrication of lead-free white-light optoelectronic devices.

Bismuth-rich oxyhalide (Bi7O9I3-Bi4O5Br2) solid-solution photocatalysts for the degradation of phenolic compounds under visible light.

HYPOTHESIS: The development of solid-solution photocatalysts with tunable bandgaps and band structures, which are significant factors that influence their photocatalytic properties, is crucial. EXPERIMENTS: We fabricated a series of novel bismuth-rich Bi7O9I3-Bi4O5Br2 solid-solution photocatalysts with controlled I:Br molar ratios (denoted as B-IxBr1-x, x  = 0.2, 0.3, 0.4, or 0.6) via a rapid, facile, and energy-efficient microwave-heating route. The photodegradations under visible-light irradiation of the phenolic compounds (4-nitrophenol (4NP), 3-nitrophenol (3NP), and bisphenol A (BPA)), and the simultaneous photodegradation of BPA and rhodamine B (RhB) in a coexisting BPA - RhB system were investigated. FINDINGS: The B-I0.3Br0.7 solid solution provided the highest photocatalytic activity toward 4NP degradation, with degradation rates 32 and 4 times higher than those of Bi7O9I3 and Bi4O5Br2, respectively. The photodegradation efficiency of the studied phenolic compounds followed the order BPA (97.5%) > 4NP (72.8%) > 3NP (27.5%). The RhB-sensitization mechanism significantly enhanced the photodegradation efficiency of BPA. Electrochemical measurements demonstrated the efficient separation and migration of charge carriers in the B-I0.3Br0.7 solid solution, which enhanced the photocatalytic activity. The B-I0.3Br0.7 solid solution effectively activated molecular oxygen to produce •O2-, which subsequently produced other reactive species, including H2O2 and •OH, as revealed by reactive-species trapping, nitroblue tetrazolium transformation, and o-tolidine oxidation experiments.

Silica nanolayer coated capillary by hydrothermal sol-gel process for amines separation and detection of tyramine in food products.

A hydrothermal sol-gel method for reproducible formation of silica nanolayer on the wall of silica capillaries was developed for electrochromatography. The formulation was optimized by observation of uniform gel formation on an optical microscope. The variables of the formulation include types of solvent, water-TEOS ratio, CTAB and urea contents, and mixing method. The procedure produced a coating of silica ca. 100 nm thick layer on the wall of the capillary. Surface morphology of the coating was characterized by SEM, contact angle and chemical composition by FT-IR spectroscopy and X-ray powder diffraction. The coating reduced the electroosmotic mobility producing enhanced separation performance. Eight standard amines (including tyramine and benzhydrylamine, as an internal standard) were separated with peak resolution Rs ≥ 2 for all adjacent peaks and plate number N ≥ 3.0 × 104 m-1. Calibration was linear from 5 to 200 µg L-1, with r2 > 0.9985 and instrumental LOD of 4.9 µg L-1. Five samples of food products were diluted and analyzed for the amines using the coated capillary and only tyramine was detected. Intra-day and inter-day precisions were less than 1.2%RSD. Percent recoveries of spiked tyramine in samples were 95 ± 3 to 106 ± 7% (n = 3).

Double Z-scheme FeVO4/Bi4O5Br2/BiOBr ternary heterojunction photocatalyst for simultaneous photocatalytic removal of hexavalent chromium and rhodamine B.

HYPOTHESIS: Fabrication of the heterojunction photocatalyst with appropriate band potentials as a promising method of inhibiting electron-hole pair recombination leading to enhanced photocatalytic properties. EXPERIMENTS: Herein, BiOBr, Bi4O5Br2, and binary BiOBr/Bi4O5Br2 composite were selectively synthesized by employing a one-step microwave irradiation method. Then, double Z-scheme FeVO4/Bi4O5Br2/BiOBr ternary composites with different weight percentages (%wt) of FeVO4 were fabricated and their photocatalytic applications were studied. The photodegradation of organic compounds (rhodamine B (RhB), methylene blue (MB) and salicylic acid (SA)), along with the photoreduction of hexavalent chromium (Cr(VI)) were investigated. FINDINGS: Comparing with the single and binary photocatalysts, and a commercial TiO2, the 1 %wt-FeVO4/Bi4O5Br2/BiOBr photocatalyst demonstrated superior visible-light-driven photocatalytic performance. In a Cr(VI)/RhB combined system, Cr(VI) photoreduction was further improved and coexisting RhB molecules were simultaneously degraded. Removal of Cr(VI) and RhB were maximized by adjusting both pH values and catalyst dosages. Based on UV-vis diffuse reflectance spectroscopy, photoluminescence spectroscopy, electrochemical investigations, active-species trapping, nitrotetrazolium blue transformation, and silver photo-deposition experiments, a double Z-scheme charge transfer mechanism with an RhB-sensitized effect was proposed. This special mechanism has led to significant enhancement in charge segregation and migration, along with higher redox properties of the ternary composite, which were responsible for the excellent photocatalytic activity.

Magnetic carbon nanofiber composite adsorbent through green in-situ conversion of bacterial cellulose for highly efficient removal of bisphenol A.

A magnetic carbon nanofiber sorbent was facilely synthesized from bio-based bacterial cellulose and FeCl3via impregnation, freeze-drying, followed by pyrolysis at 700 °C, without additional activation or nanofiber fabrication. The obtained material possessed intrinsic 3D naturally fibrous and porous structure with good magnetization. The adsorption results showed that the adsorption capacity of the prepared adsorbent towards bisphenol A (BPA) was as high as 618 mg/g, outperforming other adsorbents. Moreover, recycling the adsorbent for 10 consecutive cycles retained 96% of initial adsorption efficiency. The magnetic sorbent can maintain good magnetic properties even with recycling. Hence, the use of bacterial cellulose as a renewable carbon nanofiber precursor and FeCl3 as a source of magnetic particles, and a green pore generating agent in the present protocol, lead to a superior magnetic carbon nanofiber adsorbent with sustainable characteristics.

Direct Z-scheme FeVO4/BiOCl heterojunction as a highly efficient visible-light-driven photocatalyst for photocatalytic dye degradation and Cr(VI) reduction.

In this work, potential applications of a direct Z-scheme FeVO4/BiOCl heterojunction for photocatalytic degradation of organic dyes (methylene blue, MB and rhodamine B, RhB) and reduction of hexavalent chromium (Cr(VI)) ion under visible light irradiation were reported. Firstly, FeVO4 and BiOCl were synthesized by using a microwave heating method. Then, the FeVO4/BiOCl nanocomposites with different weight percentages of FeVO4 (1, 3, 6.25, 12.5 and 25%wt) were fabricated by a method of modified wet impregnation. The photocatalytic degradation activities of the nanocomposites were investigated in parallel with pure BiOCl and FeVO4. Among the as-prepared nanocomposites, the FeVO4/BiOCl nanocomposite with 6.25%wt of FeVO4 exhibited the highest photocatalytic dye degradation efficiency; 99.8% of RhB was degraded after being irradiated for 360 min, while 87.2% of MB was degraded. Similarly, this nanocomposite photocatalytically reduced 97.8% of Cr(VI) at a pH value of 3. The superior photocatalytic activity can be ascribed to the effective visible light absorption of the FeVO4/BiOCl heterojunction and the suppression of the recombination process of photogenerated electron-hole pairs. Additionally, the improved charge migration and separation efficiencies between FeVO4 and BiOCl through the direct Z-scheme charge transfer pathway are involved, as evidenced by the trapping experiments, and the UV-visible diffuse reflectance (UV-vis DRS), photoluminescence spectroscopy (PL) and electrochemical impedance spectroscopy analyses. Photocatalytic mechanisms of the direct Z-scheme FeVO4/BiOCl heterojunction for the photodegradation of RhB and photoreduction of Cr(VI) have been proposed and discussed in greater detail.

Green and sustainable zero-waste conversion of water hyacinth (Eichhornia crassipes) into superior magnetic carbon composite adsorbents and supercapacitor electrodes.

Troublesome aquatic weed, water hyacinth (Eichhornia crassipes) was converted into solid and liquid fractions via green and energy-saving hydrothermal carbonization (HTC). The solid product, hydrochar, was employed as a precursor to prepare magnetic carbon materials by simple activation and magnetization using KOH and Fe3+ ions, respectively. The obtained magnetic adsorbent possessed good magnetic properties and presented outstanding capacities to adsorb methylene blue (524.20 mg g-1), methyl orange (425.15 mg g-1) and tetracycline (294.24 mg g-1) with rapid adsorption kinetics even at high concentrations (up to 500 mg L-1), attributed to high specific surface area and mesopore porosity. Besides the solid hydrochar, the water-soluble liquid product was used to fabricate carbon-based supercapacitors through facile KOH activation with a considerably lower KOH amount in comparison to conventional activation. The supercapacitor electrode made from activated liquid product possessed an extremely high specific surface area of 2545 cm2 g-1 and showed excellent specific capacitance (100 F g-1 or 50 F cm-3 at 1 A g-1) and good retention of capacitance (92% even after 10 000 cycles). This work demonstrated that both solid and liquid HTC fractions from this bio-waste can serve as effective sources to prepare functional carbon materials, making this approach a sustainable zero-waste biomass conversion process.

Magnetic carbon composites with a hierarchical structure for adsorption of tetracycline, prepared from sugarcane bagasse via hydrothermal carbonization coupled with simple heat treatment process.

Sugarcane bagasse, an agricultural waste, was successfully converted into novel magnetic carbon composites by low temperature hydrothermal carbonization at 230°C for 24h, followed by heat treatment at 400°C for only 1h in air. Effects of NaOH and iron loading on the chemical properties of the composites were studied. In addition, various techniques were employed to investigate the physicochemical properties of the composites. Adsorption kinetics and isotherms were investigated with tetracycline (TC) for the magnetic composites. The magnetic carbon composite exhibited 48.35mg/g maximum adsorption capacity and was highly stable chemically and mechanically, with also good magnetic properties. The adsorption of TC by the magnetic adsorbent was mainly attributed to H-bonds and π-π interactions. The results indicate that waste sugarcane bagasse from the sugar industries can be efficiently transformed to a magnetic adsorbent for TC removal via a facile environmentally friendly method.

Carboxymethyl cellulose-assisted hydrothermal synthesis of PbS with nano- and micro-crystals.

PbS with nano- and micro-crystals was hydrothermally synthesized from Pb(NO3)2 and thiosemicarbazide using carboxymethyl cellulose (CMC) as a template at 140, 180 and 200 degrees C for 12 h. CMC, NaOH and hydrothermal temperatures have the influence on the product morphologies characterized using a scanning electron microscope (SEM) and a transmission electron microscope (TEM). PbS (cubic) composing of Pb and S was detected using an X-ray diffractometer (XRD), a selected area electron diffraction (SAED) technique and an energy dispersive X-ray (EDX) analyzer. The interpreted patterns are in accordance with those of the simulations. Raman spectrometer revealed the presence of the vibration modes at 136, 278, 432, 602 and 967 cm(-1). Emission spectra of the products were detected at 384-388 nm using a photoluminescence (PL) spectrometer.