Synthesis of ZnSe Nanocrystals for Solid-state Lighting Applications

We report the large-scale synthesis of highly luminescent ZnSe nanocrystals (NCs) by a simple and low-cost hydrothermal method. XRD (X-ray Diffraction) and HR-TEM (High Resolution Transmission Microscopy) characterization studies confirmed the formation of as-synthesized ZnSe NCs in cubic structure. The optical property of ZnSe NCs were tunable via controlling the Zn:Se molar precursor ratio (0.5:1–1.5:1), reaction temperature (150–200 0C), and reaction time (5–30 h). The resulting ZnSe NCs with the Zn:Se precursor ratio of 1:1, hydrothermally treated at 190 0C for 20 h exhibited the highest photoluminescence quantum yield obtained by PL spectra with the 355 nm excitation. The current–voltage (I–V) characteristics of the ZnSe NCs show its promising application in the solid-state lighting.

Optimization of the Mix Formulation of Geopolymer Using Nickel-Laterite Mine Waste and Coal Fly Ash

Geopolymer cement has been popularly studied nowadays compared to ordinary Portland cement because it demonstrated superior environmental advantages due to its lower carbon emissions and waste material utilization. This paper focuses on the formulation of geopolymer cement from nickel–laterite mine waste (NMW) and coal fly ash (CFA) as geopolymer precursors, and sodium hydroxide (SH), and sodium silicate (SS) as alkali activators. Different mix formulations of raw materials are prepared to produce a geopolymer based on an I-optimal design and obtained different compressive strengths. A mixed formulation of 50% NMW and 50% CFA, SH-to-SS ratio of 0.5, and an activator-to-precursor ratio of 0.429 yielded the highest 28 d unconfined compressive strength (UCS) of 22.10 ± 5.40 MPa. Furthermore, using an optimized formulation of 50.12% NMW, SH-to-SS ratio of 0.516, and an activator-to-precursor ratio of 0.428, a UCS value of 36.30 ± 3.60 MPa was obtained. The result implies that the synthesized geopolymer material can be potentially used for concrete structures and pavers, pedestrian pavers, light traffic pavers, and plain concrete.

Optimization of the Mix Formulation of Geopolymer using Nickel-laterite Mine Waste and Coal Fly Ash

Geopolymer cement has been popularly studied nowadays compared to ordinary Portland cement because it demonstrated superior environmental advantages due to its lower carbon emissions and waste material utilization. This paper focuses on the formulation of geopolymer cement from nickel-laterite mine waste (NMW) and coal fly ash (CFA) as geopolymer precursors, and sodium hydroxide (SH) and sodium silicate (SS) as alkali activators. Different mix formulations of raw materials are synthesized to produce a geopolymer based from an I-optimal design and obtained different compressive strengths. A mixed formulation of 50% NMW and 50% CFA, SH-to-SS ratio of 0.5, and an activator-to-precursor ratio of 0.429 yielded the highest 28-day unconfined compressive strength (UCS) of 22.10 ± 5.40 MPa. Furthermore, using an optimized formulation of 50.12% NMW, SH-to-SS ratio of 0.516, and an activator-to-precursor ratio of 0.428, a UCS value of 36.30 ± 3.60 MPa was obtained. The result implies that the synthesized geopolymer material can be potentially used for concrete structures and pavers, pedestrian pavers, light traffic pavers, and plain concrete.

Optimization of the Mix Formulation of Geopolymer using Nickel-laterite Mine Waste and Coal Fly Ash

Geopolymer cement has been popularly studied nowadays compared to ordinary Portland cement but has demonstrated superior environmental advantages due to its lower carbon emissions and waste material utilization. Several studies on geopolymers have utilized various wastes like fly ash, blast furnace slag, silica fume, rice husk, or a combination of these wastes. This paper presents a mix formulation design experiment to produce a geopolymer from nickel-laterite mine waste (NMW) and coal fly ash (CFA) as a geopolymer precursor, and sodium hydroxide (SH) and sodium silicate (SS) as alkali activators. An I-optimal design experiment is used to predict the compressive strength for all the mixture's possible formulations and identify optimal proportions to minimize the average variance of prediction. A mixed formulation run of 50% NMW, SH-to-SS ratio of 0.5, and an activator-to-precursor ratio of 0.4286 yielded the highest 28-day unconfined compressive strength (UCS) of 22.1±5.4 MPa. Furthermore, using an optimized formulation of 50.12% NMW, SH-to-SS ratio of 0.516, and an activator-to-precursor ratio of 0.428, an actual UCS value of 36.26±3.6 MPa was obtained. The result implies that the synthesized geopolymer material can be potentially used for pedestrian pavers, light traffic pavers, plain concrete for leveling, building bricks, ceramic glazed facing brick, and fired clay bricks.

The Effect of the Activator/Precursor Ratio on the Rheological Properties of the Alkali-activated Mining Waste Mud Paste

To determine the properties of paste, mortar or concrete, it is necessary to understand its rheological behaviour first. This study discusses the effect of the activator/precursor ratio on the rheological properties of the alkali-activated paste. The pastes consisted of a mix of 70 % of tungsten mining waste mud, 15% waste glass and 15% of metakaolin. This mix was activated by combining sodium hydroxide and sodium silicate. Five activator/precursor (a/p) ratios were studied: 0.37, 0.38, 0.39, 0.40 and 0.41. The result obtained shows that the rheology of the pastes is affected by the activator/precursor ratio. The rheological behaviour of the paste fits the Bingham model. The yield stress (τ0) and plastic viscosity (μ) increase inversely with the activator/precursor ratio (e.g. a/p=0.37 gives τ0=84.19 and μ=0.4185; a/p=0.41 gives τ0=30.389 and μ=0.2937). The workability increases proportionally with the activator/precursor ratio (e.g. a/p=0.37 gives a slump=133 mm; a/p=0.41 gives a slump=158 mm). The compressive strength decreases when the activator/precursor ratio increases (e.g. at 28 days for a/p=0.37, the compressive strength was 19.6 MPa; for a/p=0.41, the compressive strength was 13 MPa). Finally, the ideal ratios were 0.38 and 0.39.

The systematic study of the precursor ratio effect in the Cd–Zn–S quantum dot synthesis

The controllable synthesis of highly photoluminescent Cd–Zn–S QDs with application of novel N-phenylmorpholine-4-carbothioamide as an eco-friendly sulphur source.

Influence of precursor ratio and dopant concentration on the structure and optical properties of Cu-doped ZnCdSe-alloyed quantum dots

Tunable copper doped Zn1−xCdxS alloy quantum dots (QDs) were successfully synthesized by the wet chemical method.