Nanostructured materials have received great interest due to their fascinating physical, optical, electrical, and thermoelectric properties as well as their potential applications in nanodevices [1–4]. Metal borates are considered among the most important of these materials because of their unique properties, such as their light weight, high strength, high heat-resistance, corrosion-resistance, and high coefficient of elasticity, etc. Hence, the nanoscale metal borates are ideal for exploring their potential applications in the fields of nanocomposites, nanomechanics, and nano-electronics. Among the various metal borates, aluminum borate is perhaps the best known ceramic material with chemical stability, enhanced mechanical properties and potential applications in high-temperature composites . Magnesium borate is another remarkable ceramic material that shows excellent mechanical and thermal properties.
Magnesium borate hydroxide (MgBO2(OH)), also known as the Szaibelyite, is a widely available translucent mineral in nature and is used as the main source of boron in industry [6, 7]. The Szaibelyite is also an important source of anhydrous magnesium borate . Magnesium borate can be used as thermo-luminescent phosphor , antiwear and friction reducing additive , ferro-elastic material , which is a candidate for tunable laser applications , and can be used as a luminescent material for fluorescent discharge lamps, cathode ray tube screens, and X-ray screens . Recently variety of magnesium borate nanostructures such as nanorods , nanowires [15, 16], nanobelts , nanoparticles  and nanotubes  have been fabricated by different synthesis techniques including thermal evaporation, chemical vapor deposition, ethanol supercritical fluid drying technique, and thermal evaporation in IR-irradiation heating furnace [10, 14–18]. However, in all these reported routes, the synthesis was performed at high temperatures (750–1,100 °C).
The synthesis of nanoparticles with controlled size and shape results in new electronic and optical properties, which is suitable for many electronic and optoelectronic applications . The use of surfactants as stabilizers has advantages with the fact that these surface-active chemicals possess sufficient strength to effectively control the particle size growth. The surfactants support to have particles with “monodisperse” size distribution and increased aspect ratio, and they also effectively prevent the particles from agglomeration [20–23]. Over the decades, the hydrothermal process has proved to be one of the most successful methods for synthesizing low dimensional materials. However, there exist very few reports on the synthesis of nanostructured MgBO2(OH) using the hydrothermal method [8, 24–26]. In addition, the conversion of magnesium borate hydroxide to anhydrous magnesium borate is rarely reported [7, 21]. Zhu et al. [8, 24, 25] reported the hydrothermal synthesis of MgBO2(OH) nanowhiskers using MgCl2, H3BO3 and NaOH as the starting materials with molar ratio of Mg:B:Na as 2:3:4 at 240 °C for 18 h. Zhu et al.  also investigated the effect of the dropping rate of NaOH into the precursor solution, droplet size, and amount of the NaOH solution and the hydrothermal reaction time on the hydrothermal formation of the MgBO2(OH) nanowhiskers with other synthesis parameters kept constant. The morphology preservation and crystallinity improvement in the thermal conversion of the hydrothermal synthesized MgBO2(OH) nanowhiskers to Mg2B2O5 nanowhiskers was investigated in the temperature range of 650–700 °C and was kept under isothermal condition for 2.0–4.0 h . Xu et al.  demonstrated the growth of magnesium borate (Mg2B2O5) nanorods at 400 °C (supercritical condition) by solvothermal route and explained that the temperature of 200 °C was not sufficient for synthesizing the well-defined nanostructures. In addition, the synthesis of the magnesium borate nanorods needs the assistance of surfactants/capping agents. In their work, the MgBO2(OH) columnar-like particles were synthesized at 320 °C with ethanol and water as solvents. In the present work, the MBH nanowhiskers with regular shape and size were successfully synthesized at a reaction temperature of 200 °C (H2O as solvent) without using any surfactants/capping agents. Additionally, the effect of surfactants on the structure and surface morphology of the MBH nanomaterials is studied. Optical properties including UV–vis absorption and photoluminescence (PL) of the MBH nanowhiskers are also investigated.