Optimization of phosphogypsum conversion into calcium carbonate and lithium sulfate monohydrate

Phosphogypsum (PG) is an acidic by-product generated during the production of phosphoric acid. Usually this by-product is stockpiled or dumped into water bodies, which causes several environmental pollution problems. The aim of this work is to reduce this environmental risk by producing CaCO3 and Li2SO4.H2O from the conversion of PG by Li2CO3. To optimize the reaction conditions, four parameters have been investigated such as the initial concentration of the reagents, the reaction duration, the temperature and the gypsum purity. In addition, the nature of the resulting products was proved principally by X-ray diffraction technic. The obtained results show that the initial concentration of the reagents and the reaction duration are the most influential parameters, while the temperature has no significance effect on this reaction. Also, the acidity and the presence of impurities into PG induce its reactivity compared than commercial gypsum. The purity of the formed CaCO3 and Li2SO4.H2O at the optimum conversion of PG is 96.08 and 98.71% respectively.

The Incorporation of Amplified Metal-Enhanced Fluorescence in a CMOS-Based Biosensor Increased the Detection Sensitivity of a DNA Marker of the Pathogenic Fungus Colletotrichum gloeosporioides

Half of the global agricultural fresh produce is lost, mainly because of rots that are caused by various pathogenic fungi. In this study, a complementary metal-oxide-semiconductor (CMOS)-based biosensor was developed, which integrates specific DNA strands that allow the detection of enoyl-CoA-hydratase/isomerase, which is a quiescent marker of Colletotrichum gloeosporioides fungi. The developed biosensor mechanism is based on the metal-enhanced fluorescence (MEF) phenomenon, which is amplified by depositing silver onto a glass surface. A surface DNA strand is then immobilized on the surface, and in the presence of the target mRNA within the sample, the reporter DNA strand that is linked to horseradish peroxidase (HRP) enzyme will also bind to it. The light signal that is later produced from the HRP enzyme and its substrate is enhanced and detected by the coupled CMOS sensor. Several parameters that affect the silver-deposition procedure were examined, including silver solution temperature and volume, heating mode, and the tank material. Moreover, the effect of blocking treatment (skim milk or bovine serum albumin (BSA)) on the silver-layer stability and nonspecific DNA absorption was tested. Most importantly, the effect of the deposition reaction duration on the silver-layer formation and the MEF amplification was also investigated. In the study findings a preferred silver-deposition reaction duration was identified as 5–8 min, which increased the deposition of silver on the glass surface up to 13-times, and also resulted in the amplification of the MEF phenomenon with a maximum light signal of 50 relative light units (RLU). It was found that MEF can be amplified by a customized silver-deposition procedure that results in increased detection sensitivity. The implementation of the improved conditions increased the biosensor sensitivity to 3.3 nM (4500 RLU) with a higher detected light signal as compared to the initial protocol (400 RLU). Moreover, the light signal was amplified 18.75-, 11.11-, 5.5-, 11.25-, and 3.75-times in the improved protocol for all the tested concentrations of the target DNA strand of 1000, 100, 10, 3.3, and 2 nM, respectively. The developed biosensor system may allow the detection of the pathogenic fungus in postharvest produce and determine its pathogenicity state.

Comparisons of metal oxides activity in the transesterification of triglycerides by С1–С4 alcohols

The activity of heterogeneous catalysts for the transesterification reaction of sunflower oil triglycerides with aliphatic alcohols of normal structure was investigated in this work. Fine-dispersed oxides ZnO, NiO, FeO, CuO and MnO served as catalysts. The following aliphatic alcohols were used in the transesterification process of sunflower oil triglycerides: methanol, ethanol, propan-1-ol and butan-1-ol. The transesterification reaction was performed under the conditions as follows: the content catalyst of 0.25 wt.%, the triglycerides:alcohol molar ratio of 6.5:1 and the temperature of 333 K (methanol) or 348 K (ethanol, propan-1-ol and butan-1-ol). The investigated metal oxides were arranged in series according to their activity towards the transesterification reaction of sunflower oil triglycerides with C1–C3 alcohols. It was established that these series were practically the same for the mentioned alcohols. Similarity between the oil conversion curves of the reaction duration for C1–C3 aliphatic alcohols in the presence of all studied catalysts was shown. The use of the most active catalysts (ZnO and NiO) for the transesterification reaction of triglycerides with C1–C3 aliphatic alcohols allowed achieving the triglycerides conversion of more than 95% at the reaction duration of 2.5 h. Iron and manganese oxides exhibited relatively high catalytic activity in the transesterification reaction with aliphatic C1–C2 alcohols. However, the oil conversion was only 86.7–91.1% for the transesterification reaction by propan-1-ol in the presence of above-mentioned catalysts under the optimal conditions (reaction duration of 2.5 h). Copper oxide exhibited the lowest activity among all catalysts that were tested. The highest initial reaction rate in the presence of metal oxides was achieved in the transesterification of sunflower oil triglycerides by methanol. The reaction rate of triglycerides transesterification by butan-1-ol was by three orders of magnitude lower than that achieved by using of other alcohols.

Supermagnetic Nano-Bifunctional Catalyst from Rice Husk: Synthesis, Characterization and Application for Conversion of Used Cooking Oil to Biodiesel

The present work investigated the biodiesel production from used cooking oil catalyzed by nano-bifunctional supermagnetic heterogeneous catalysts (RHC/K2O/Fe) derived from rice husk doped with K2O and Fe synthesized by the wet impregnation method. The synthesized catalysts (RHC/K2O/Fe) were characterized for crystallinity by X-ray diffraction spectroscopy (XRD), total acidity and basicity using CO2/NH3-TPD, textural properties through Brunauer-Emmett-Teller (BET), thermal stability via thermogravimetric analyzer (TGA), functional group determination by Fourier-transform infrared spectroscopy (FTIR), surface morphology through field emission scanning electron microscopy (FESEM), and magnetic properties by vibrating sample magnetometer (VSM). The VSM result demonstrated that the super-paramagnetic catalyst (RHC/K2O-20%/Fe-5%) could be simply separated and regained after the reaction using an external magnetic field. The operating conditions such as catalyst loading, methanol/oil molar ratio, temperature, and reaction duration were studied. The screened RHC/K2O-20%/Fe-5% catalyst was selected for further optimization and the optimum reaction parameters found were 4 wt % of catalyst, a molar ratio of methanol/oil of 12:1, 4 h reaction duration, and 75 °C reaction temperature with a maximal yield of 98.6%. The reusability study and reactivation results revealed that the nano-bifunctional magnetic catalyst (RHC/K2O-20%/Fe-5%) could be preserved by high catalytic activity even after being reused five times.

An Efficient Synthesis and Photoelectric Properties of Green Carbon Quantum Dots with High Fluorescent Quantum Yield

To greatly improve the production quality and efficiency of carbon quantum dots (CQDs), and provide a new approach for the large-scale production of high-quality CQDs, green carbon quantum dots (g-CQDs) with high product yield (PY) and high fluorescent quantum yield (QY) were synthesized by an efficient one-step solvothermal method with 2,7-dihydroxynaphthalene as the carbon source and ethylenediamine as the nitrogen dopant in this study. The PY and QY of g-CQDs were optimised by adjusting reaction parameters such as an amount of added ethylenediamine, reaction temperature, and reaction duration. The results showed that the maximum PY and QY values of g-CQDs were achieved, which were 70.90% and 62.98%, respectively when the amount of added ethylenediamine, reaction temperature, and reaction duration were 4 mL, 180 °C, and 12 h, respectively. With the optimised QY value of g-CQDs, white light emitting diodes (white LEDs) were prepared by combining g-CQDs and blue chip. The colour rendering index of white LEDs reached 87, and the correlated colour temperature was 2520 K, which belongs to the warm white light area and is suitable for indoor lighting. These results indicate that g-CQDs have potential and wide application prospects in the field of white LEDs.

The Investigation of Some Factors Influencing to the For-mation of Monocalcium Phosphate in Aqueous Medium

Some factors that influence to the formation of monocalcium phosphate in aqueous solution have been investigated in detail. The results show that reaction temperature, and initial concentration of phosphoric acid, as well as reaction duration determine the content of monocalcium phosphate in the processing mixture. The information in this report will be useful, and the basis for the design of the synthesis reactor in the monocalcium phosphate production

Reaction duration-dependent formation of two Cu(ii)-MOFs with selective adsorption properties of C3H4 over C3H6

Reaction duration was found to play an important role in the formation of two different MOFs, BUT-301 and BUT-302, which all show three-dimensional framework structures, permanent porosity and selective adsorption properties of C3H4 over C3H6.

Effect of Temperature, pH, and Reaction Duration on Microbially Induced Calcite Precipitation

In this study, the amount of calcite precipitate resulting from microbially induced calcite precipitation (MICP) was estimated in order to determine the optimal conditions for precipitation. Two microbial species (Staphylococcus saprophyticus and Sporosarcina pasteurii) were tested by varying certain parameters such as (1) initial potential of hydrogen (pH) of urea-CaCl2 medium, (2) temperature during precipitation, and (3) the reaction duration. The pH values used for testing were 6, 7, 8, 9, and 10, the temperatures were 20, 30, 40, and 50 °C, and the reaction durations were 2, 3, and 4 days. Maximum calcite precipitation was observed at a pH of 7 and temperature of 30 °C. Most of the precipitation occurred within a reaction duration of 3 days. Under similar conditions, the amount of calcite precipitated by S. saprophyticus was estimated to be five times more than that by S. pasteurii. Both the species were sensitive to temperature; however, S. saprophyticus was less sensitive to pH and required a shorter reaction duration than S. pasteurii.