White LED Bulbs Research Articles

A comprehensive aqueous processing of waste LED light bulbs to recover valuable metals and compounds

White LED bulbs contain significant quantities of Cu, Sn, Pb, Al and appreciable amounts of Ga and traces of In. A feasible recovery of the valuable components – either in metallic or compound forms - has been devised and examined. Leaching the assemblies with 4 M HNO3 at 80 °C could leach Cu, Fe, Pb and Ag, while Al is passivated and Sn precipitates. In this step, the LED beads are detached from the aluminium base plates. The solid residue comprises of practically pure Al plates and Sn(OH)4. Pure Cu hydroxide was recovered by precipitation. The physically liberated solid bodies of the detached LED beads were roasted to convert Ga and In into soluble compounds. While a simple oxidative roasting could assure ∼80% recovery, alkaline fusion with NaOH or roasting with Na2CO3 yielded >90% recoveries. Leaching the roasted material with 1–6 M NaOH could efficiently dissolve Ga, while In was only slightly attacked. However, the major portion of In could be leached by applying as high as 10–11 M NaOH with similar efficiencies. Finally, the extractions of Ga and In were studied by electrowinning from the alkaline solutions yielding 99.99% pure Ga and 99.9% pure In deposits, respectively.

Design of ZIF-67 nanoflake derived NiCo-LDH/rGO hybrid nanostructures for aqueous symmetric supercapattery application under alkaline condition

Well-defined polyhedral ZIF-67 metal-organic frameworks (MOFs) are usually synthesized using methanol as solvent. In this work, methanol is replaced with deionized water as a solvent to synthesize ZIF-67 MOFs with unique nanoflake morphology. The ZIF-67 nanoflakes are synthesized directly by in situ method on reduced graphene oxide (rGO) to obtain ZIF-67/rGO-x precursors which are further transformed into NiCo-layered double hydroxide nanocomposites (NiCo-LDH/rGO-x, x = 10, 30, 50 and 90 mg of rGO). The NiCo-LDH/rGO-x nanostructured composites are found to be excellent materials for battery type supercapacitor (supercapattery) applications. Among these samples, the NiCo-LDH/rGO-30 composite gives maximum specific capacity of 829 C g−1 (1658 F g−1) at a current density of 1 A g−1 and high rate capability. The as fabricated 2-electrode symmetric Swagelok device delivered a high energy density of 49.2 Wh kg−1 and a power density of 4511 W kg−1, and enabled us to glow red, blue and white LED bulbs using three coin cells. The device can show good capacity retention even after 3000 continuous charge–discharge cycles. The NiCo-LDH/rGO-30 composite, in situ derived from ZIF-67 MOF in combination with optimal amount of rGO, is an excellent material to deliver both high energy density and high power density in supercapattery devices.

The influence of LED and fluorescent lamps on the growth and development of stone fruit rootstocks in Vitro

This research project is about the advantages and disadvantages of using white LED bulbs and fluorescent lamps when growing fruit rootstocks (VSL -2 fruit rootstock) in Vitro. The comparative analysis of using two different lamps will be based on subject of plant growing, development of root system and green leaf pigmentation. Moreover, pros and cons are summed up in terms of the resulting plant yield, where LED bulbs and fluorescent lamps were used within different illumination.