Upcycling waste derived glass into high-performance photocatalytic scaffolds by alkali activation and direct ink writing.

Novel and eco-friendly solutions are extensively needed for wastewater treatment. This work capitalizes on the combination of waste vitrification and additive manufacturing to produce an efficient photocatalyst for the specific purpose. Fine powders of waste-derived glass, containing Fe3O4 inclusions, by simple suspension (for a solid loading of 65 wt %) in alkaline solution (5 M NaOH), were transformed into pastes for direct ink writing. 3D-printed reticulated scaffolds were stabilized by the progressive hardening of a zeolite-like gel, formed by glass/solution interaction, at nearly room temperature. The printed scaffolds were successfully tested for the removal of methylene blue, realized by combining the high sorption capacity of the gel with the catalytic activity of magnetite inclusions, under UV light. A complete degradation of methylene blue is achieved by 90 min exposure, comparing favorably with other reported photocatalytic materials, requiring from 60 to 360 min. The photocatalytic activity was tested for several cycles, with no significant degradation. In other words, a waste-derived material can be reused for multiple times, to remediate wastewaters, with evident benefits on waste minimization.

Upcycling of Pharmaceutical Glass into Highly Porous Ceramics: From Foams to Membranes.

The present COVID-19 emergency has dramatically increased the demand for pharmaceutical containers, especially vials. End-of-life containers, however, cannot be easily recycled in the manufacturing of new articles. This paper presents some strategies for upcycling of pharmaceutical glass into various porous ceramics. Suspensions of a fine glass powder (70 vol%) are used as a starting material. Highly uniform cellular structures may be easily prepared by vigorous mechanical stirring of partially gelified suspensions with added surfactant, followed by drying and firing at 550-650 °C. Stabilization of the cellular structures at temperatures as low as the glass transition temperature (Tg) of the used glass is facilitated by thermal decomposition of the gel phase, instead of viscous flow sintering of glass. This finding enabled the preparation of glass membranes (∼78 vol% open porosity), by direct firing of hardened suspensions, avoiding any surfactant addition and mechanical stirring. The powders obtained by crushing of hardened suspensions, even in unfired state, may be used as a low-cost sorbent for dye removal.

Highly fluorescent carbon dots derived from Mangifera indica leaves for selective detection of metal ions.

In this study, we report an inexpensive, green, and one-pot synthesis method for highly fluorescent carbon quantum dots (CQDs) using mango (Mangifera indica: M. indica) leaves to develop an efficient sensing platform for metal ions. The CQDs synthesized from M. indica leaves via pyrolysis treatment at 300 °C for 3 h were characterized by various spectroscopic and electron microscopy techniques for their structural, morphological, and optical properties. Accordingly, the synthesized CQDs showed an absorption peak at 213 nm to confirm the p-p* transition of the carbon core state, while the CQD particles were spherical with a size less than 10 nm. The prepared CQDs showed excellent fluorescent properties with blue emission spectra (around 525 nm) upon excitation at 435 nm. The synthesized CQDs had the prodigious sensing potential to detect Fe2+ ions in water with a limit of detection of 0.62 ppm. Additionally, their sensing capability was tested using a real sample (e.g., Livogen tablet). Moreover, the synthesized CQDs showed substantial stability over a long period (three months). Thus, this study provides an inexpensive and facile method for CQD-based sensing of Fe2+ ions with a photoluminescence quenching mechanism.

Visible-light-induced enhanced photocatalytic degradation of Rhodamine-B dye using BixSb2-xS3 solid-solution photocatalysts.

The present work examines binary solid solutions of BixSb2-xS3 [x = 0.536, 1.09, 1.68] toward photocatalytic degradation of Rhodamine-B (RhB) under visible light. Phase and microstructural analysis confirmed the formation of Bi0.536Sb1.464S3, Bi1.09Sb0.91S3, and Bi1.68Sb0.32S3 solid-solution phase with nanorods (~25-50 nm average diameter) morphology. The synthesized products show outstanding photocatalytic degradation of RhB with ~95-99.5% degradation achieved within 30 min. The kinetic study finds the high degradation efficiency (~98%) of BixSb2-xS3 photocatalysts stems from the amenable band gap (~2.3 eV, confirmed from DRS study), and higher separation efficiency of photogenerated electron-hole pairs (established from PL studies). The complete detoxification of RhB dye was confirmed by quantitative estimation of CO2 post photodegradation through GC analysis. Moreover, due to the solid and hard nature of the photocatalysts, it was easily recovered from the reaction mixture and reused multiple times without losing the degradation behavior. The parallel comparison with other active photocatalysts demonstrates BixSb2-xS3 [x = 0.536, 1.09, 1.68] have higher catalytic efficiency with similar dosing hitherto reported in the literature and possibly can be used for degradation of other organic dyes using the visible spectrum.

Band gap tuning and surface modification of carbon dots for sustainable environmental remediation and photocatalytic hydrogen production - A review.

Energy and water are the two major issues facing the modern mankind. Providing freshwater requires energy and producing energy uses water. In the present-day scenario, both these routes face growing problems and limitations. Energy crisis has risen due to the depletion of fossil fuels that cause pollution to water bodies making the water unusable for human consumption. In this regard, semiconductor nanocrystals with luminescent properties or carbon quantum dots (CQDs) are the newly developed nanomaterials whose distinctive photo-physical characteristics are focusing to a new generation of robust materials and sensors for sustainable development. In this review, advances in surface and band gap modification of CQDs to improve the activity of nanomaterials will be discussed with special reference to some specific CQDs exhibiting special optical properties for water treatment/splitting applications. Recent advances on CQDs nanocomposites including their applications in photodegradation of organic pollutants, sensing of heavy metal ions in water and water splitting are discussed critically to narrate the future prospects in this field. Challenges and limitations for further improvement are covered to provide smart choices for creating sustainability of benign environment and economic benefits.

Amphiphilic carbon dots derived by cationic surfactant for selective and sensitive detection of metal ions.

Carbon Dots (CDs) the kind of recently exposed fluorescent nanomaterials have become increasingly popular in the precedent decade due to their distinctive physical and optical properties. Relating to above recognition for the first time we present the synthesis of CDs by cationic surfactant, Cetylpyridinium Bromide (CPB). Due to good carbon content amphiphilicity, and existence of heteroaromatic π system, CPB reveals three advantageous properties including a good carbon source, stabilizing agent, and contributing fluorophore in the CDs system. The as prepared CDs synthesized by hydrothermal technique reveals excellent fluorescent properties having strong green emission at 525 nm when excited over 470 nm. The FTIR results showed the presence of CC, CO, NH, CH and OH bonds. The presence of hydrophilic groups such as carboxyl and hydroxyl groups present on the surface confer them water solubility. The HRTEM results revealed the size of prepared CDs to be in the range of 7-10 nm. The XPS spectrum confirms the presence of Carbon, Oxygen and Nitrogen, suggesting that the CDs have good purity and very little impurities. Latterly CDs were used for the selective and sensitive detection towards Fe2+ ions. Also the as prepared CDs were utilized for real sample analysis.

Effect of Surfactants on the Structure and Adsorption Efficiency of Hydroxyapatite Nanorods.

Porous hydroxyapatite (HAp) nanorods using surfactant templating proceeded via microwave irradiation method. Study of BET surface area measurement of the HAp nanorods showed that surface area of HAp nanorods with a mixture of cat-anionic surfactants was higher (56.16 m2/g) than their individual counterpart (for anionic 52.8 m2/g and for cationic 48.8 m2/g) as well as without surfactant (19.07 m2/g) due to higher synergistic effect and low critical aggregation concentration of the mixture. Surfactant-directed synthesis of porous HAp has been explored in literature, but the relation between the pore size distribution, surface area and morphology and choice of surfactant(s) was not fully understood and hence in this work we have explored those parameters. The rod shape morphology and the crystal structure of the synthesized HAp nanomaterial were observed by FESEM, HRTEM, and XRD. Due to the higher surface area, HAp nanorods synthesized from the cat-anionic mixture, act as a better adsorbent for dyes and metal ions. The maximum adsorption of dye (methylene blue) was found to be 833.3 mg/g whereas for heavy metal ions like Pb2+ and Cd2+ were 909 and 714.28 mg/g respectively. The kinetic mechanism, the effects of adsorbate pH, temperature, contact time and adsorbent concentration on the dye and metal ions removal were also explored. The antibacterial property of HAp nanorods after doping with silver was investigated against the gram-negative Escherichia coli and gram-positive Bacillus subtilis bacteria by measuring minimal inhibitory concentration (MIC) method.

A sensitive turn on fluorescent probe for detection of biothiols using MnO2@carbon dots nanocomposites.

Presently, the combination of carbon quantum dots (CQDs) and metal oxide nanostructures in one frame are being considered for the sensing of purine compounds. In this work, a combined system of CQDs and MnO2 nanostructures was used for the detection of anticancer drugs, 6-Thioguanine (6-TG) and 6-Mercaptopurine (6-MP). The CQDs were synthesized through microwave synthesizer and the MnO2 nanostructures (nanoflowers and nanosheets) were synthesized using facile hydrothermal technique. The CQDs exhibited excellent fluorescence emission at 420nm when excited at 320nm wavelength. By combining CQDs and MnO2 nanostructures, quenching of fluorescence was observed which was attributed to fluorescence resonance energy transfer (FRET) mechanism, where CQDs act as electron donor and MnO2 act as acceptor. This fluorescence quenching behaviour disappeared on the addition of 6-TG and 6-MP due to the formation of Mn-S bond. The detection limit for 6-TG (0.015µM) and 6-MP (0.014µM) was achieved with the linear range of concentration (0-50µM) using both MnO2 nanoflowers and nanosheets. Moreover, the as-prepared fluorescence-sensing technique was successfully employed for the detection of bio-thiol group in enapril drug. Thus a facile, cost-effective and benign chemistry approach for biomolecule detection was designed.

Microwave Treated Bentonite Clay Based TiO2 Composites: An Efficient Photocatalyst for Rapid Degradation of Methylene Blue.

The composites of TiO2 and bentonite were synthesized under microwave conditions. Formation of anatase TiO2 nanoparticles was achieved within 10 minutes by microwave treatment at 180 °C on the clay surface. Phase composition, particle morphology, specific surface area, chemical bonding etc. of these samples were characterized by using X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), nitrogen gas adsorption method (BET) and fourier transform infrared spectroscopy (FTIR). The photo catalytic activity of the as prepared material to degrade methylene blue resulting in complete photomineralization to CO2 and H2O was monitored by UV-Vis spectroscopy and gas chromatography. The effect of TiO2 content on the photocatalytic activity was also investigated. Bentonite containing 50% TiO2 by weight showed the highest photocatalytic activity because of its relatively large specific surface area and pore volume. Overall our findings show that the photocatalytic activity of resulting composite is more efficient than commercial nano-TiO2 and thus could therefore be an economic competitive candidate for contaminated water remediation.