Direct Synthesis of Nanosized NiCo₂O₄Spinel and Related Compounds via Continuous Hydrothermal Synthesis Methods

Abstract

A series of crystalline homometallic and heterometallic cobalt and nickel hydroxides and oxides were prepared using a continuous hydrothermal flow synthesis system. In all syntheses, the relevant metal salt solutions were pumped under high pressure to meet pH or other chemical modifiers (H 2 O 2 or PVP) before the mixture was brought into contact with a feed of superheated (or supercritical) water, whereupon precipitation and particle growth occurred. The resulting nanoparticle (typically less than 100 nm in diameter) suspensions were collected from the outlet of the back-pressure regulator of the hydrothermal system. The collected suspensions were centrifuged, and the washed solids were freeze-dried prior to analyses. The nanopowders were characterized by a number of analytical methods including X-ray powder diffraction, Brunauer-Emmett-Teller (BET) surface area measurements, and simultaneous thermogravimetric analysis/differential scanning calorimetry.

Direct continuous hydrothermal synthesis of high surface area nanosized titania

“…1) [25][26][27][28]. Briefly, the details of the system are as follows: the CHFS system incorporates three Gilson 305 HPLC pumps fitted with 25 mL pump-heads, 316SS Swagelok TM 1/8" stainless steel fittings and tubing (except for the counter-current mixing point) and a 2000 W electrically powered water preheater which were built from 1/4" fittings.…”

“…The supercritical water feed was heated to 400 • C, whilst the other feeds were at room temperature initially, the entire system was pressurised to 24.1 MPa. The third cold water feed (P3) was used to give in-line dilution and in order that direct comparisons could be made to related work where this pump was used to add certain oxidants or pH modifiers [25][26][27][28] (although these chemicals were not added in this work).…”

Photocatalytic activities of N-doped nano-titanias and titanium nitride

“…1). [45][46][47][48][49] Briefly, the details of the system are as follows; the CHFS system incorporates three Gilson 305 HPLC pumps fitted with 25 mL pump-heads, 316SS Swagelok TM 1/8 in. fittings and tubing, except the counter-current mixing point (R in Fig.…”

Rapid Production of Micro- and Nano-particles Using Supercritical Water

“…Nickel and cobalt based nanomaterials are of interest in catalysis as inexpensive replacements for noble metal catalysts [87]. Nickel particles with diameters under 600 nm were synthesized rapidly and continuously in water at 573∼653 K and 30 MPa.…”

“…A series of crystalline homometallic and heterometallic cobalt and nickel, hydroxides and oxides (typically less than 100 nm in diameter) were prepared using a continuous hydrothermal flow synthesis system [87]. Organic reagents such as R-COOH and R-NH 2 were used to in-situ modify organic surface of cobalt aluminate nanoparticles in SCW.…”