Influence of process parameters on hydrothermal formation of magnesium borate hydroxide nanowhiskers

Abstract

Uniform magnesium borate hydroxide [MgBO 2 (OH)] nanowhiskers with a diameter of 20-60 nm and an aspect ratio of 10-70 were synthesised via a coprecipitation/hydrothermal reaction route, using NaOH, MgCl 2 and H 3 BO 3 as the reactants. The experimental results indicated that the control of the Mg/B/Na molar ratio at 2 : 3 : 4, the decrease in the NaOH concentration from 2?0 to 0?33 mol L -1 , the increase in the hydrothermal temperature from 160 to 240uC and the prolongation of the hydrothermal reaction time from 2?0 to 30?0 h could promote the growth of the MgBO 2 (OH) nanowhiskers along the c axis, leading to the formation of the MgBO 2 (OH) nanowhiskers with high aspect ratio.

Hydrothermal Formation of the Head-to-Head Coalesced Szaibelyite MgBO2(OH) Nanowires

“…The interplanar spacings of 0.597 nm detected from the legible lattice fringes along the axis of the nanowire (Fig. 3b 1 ) was quite similar to that of the (200) planes of the standard MgBO 2 (OH), indicating the preferential growth direction of the nanowires parallel to the (200) planes, in agreement with that of the MgBO 2 (OH) nanowhiskers along the c -axis [38] and also the growth habit of the natural szaibelyite (MgBO 2 (OH)) [40]. The statistic data showed that the MgBO 2 (OH) nanowires had a length of 0.5–9.0 μm (approx.…”

“…Since low concentration of the reactants, relatively long reaction time and high temperature favored the synthesis of MgBO 2 (OH) nanowhiskers with a longer size and higher aspect ratio [38], less amount of NaOH solution (4 mol L −1 ), in other words, lower initial concentration of NaOH (0.17 mol L −1 ) was employed in the room temperature coprecipitation so as to further increase the length and aspect ratio of the hydrothermal product, with the molar ratio of Mg:B:Na and also total volume of the mixed solution unchanged. The resultant well dispersed uniform nanowires (Fig.…”

“…The effect of the feeding mode on the hydrothermal product indicated that slow dropping rate (0.5 d s −1 ) and small droplet size (0.02 mL d −1 ) of the dropwise added NaOH solution were favorable for enlarging the aspect ratio of the hydrothermal product thus could promote the 1D growth of the MgBO 2 (OH) nanostructures during the subsequent hydrothermal treatment. Since low concentration of the reactants, relatively long reaction time and high temperature favored the synthesis of MgBO 2 (OH) nanowhiskers with a longer size and higher aspect ratio [ 38 ], less amount of NaOH solution (4 mol L −1 ), in other words, lower initial concentration of NaOH (0.17 mol L −1 ) was employed in the room temperature coprecipitation so as to further increase the length and aspect ratio of the hydrothermal product, with the molar ratio of Mg:B:Na and also total volume of the mixed solution unchanged. The resultant well dispersed uniform nanowires (Fig.…”

“…In the previous work, uniform MgBO 2 (OH) nanowhiskers (diameter: 20–50 nm, length: 0.5–3 μm) were hydrothermally synthesized (240 °C, 18 h), using MgCl 2 · 6H 2 O, H 3 BO 3 , and NaOH as the reactants [ 33 ]. Based on the understanding of the effect of the process parameters on the diameter, length, and aspect ratio of the hydrothermal product [ 38 ], herein we report for the first time the significant effect of the feeding mode on the morphology and size distribution of the hydrothermal product, which resulted in the head-to-head coalesced MgBO 2 (OH) nanowires with a length of 0.5–9.0 μm, a diameter of 20–70 nm, and an aspect ratio of 20–300 in absence of any capping reagents/surfactants or seeds. The feeding mode-intensified 1D preferential growth was also helpful for the wet chemistry based synthesis of other 1D nanostructured materials, especially for those with anisotropic crystal structures.…”

Morphology preservation and crystallinity improvement in the thermal conversion of the hydrothermal synthesized MgBO2(OH) nanowhiskers to Mg2B2O5 nanowhiskers

“…In addition to the parameters in course of thermal conversion, the hydrothermal procedure [49] determined the 1D morphology of the MgBO 2 (OH) nanowhiskers and could further influence the morphology of the final calcined Mg 2 B 2 O 5 nanowhiskers. Hydrothermal conditions are favorable for the formation of the unique crystal structure containing water in lattice; the unique structure can contribute to porous structure by dehydration and the active porous whiskers can finally form high-crystallinity nanowhiskers via recrystallization.…”