A comment on: “Conventional and Microwave Hydrothermal Synthesis and Application of Functional Materials: A Review”

Abstract

In the recent paper published in Materials (Yang et al., 2019), there is a mistake in the explanation of crystal growth mechanism of the hydrothermal method. The error in this article is discussed in this short communication.

One‐step synthesis of flower‐like η‐Al 2 O 3 via supercritical hydrothermal method

“…For achieving the η‐Al 2 O 3 phase, the experiments were carried out at 500°C in this research. Owing to the increase in high temperature, nucleation and growth rates the precipitate formation is accelerated [44]. As it was discussed before, the increased time caused particles' secondary growth at high temperature.…”

A Review of Microwave Synthesis of Zinc Oxide Nanomaterials: Reactants, Process Parameters and Morphologies

“…The heating of substances by microwave radiation has already been thoroughly described in the literature by numerous scholars [ 428 , 429 , 430 , 431 , 432 , 433 , 434 , 435 , 436 , 437 , 438 , 439 , 440 , 441 , 442 , 443 , 444 , 445 , 446 , 447 , 448 , 449 , 450 , 451 , 452 , 453 , 454 , 455 , 456 , 457 ]. Microwave heating (MH) is based on the transformation of electromagnetic field energy stemming from microwave radiation into kinetic energy (heat) by interacting with the polar particles of the material.…”

“… Rapid heating with preservation of low thermal gradients (rapid energy transfer) [ 468 ]. Heating uniformity (which is translated into the quality of obtained products, e.g., homogeneity and narrow size distribution of obtained nanomaterials [ 437 , 438 , 439 , 440 , 441 , 469 , 470 ]). Shorter duration of syntheses/processes.…”

“…Heating uniformity (which is translated into the quality of obtained products, e.g., homogeneity and narrow size distribution of obtained nanomaterials [ 437 , 438 , 439 , 440 , 441 , 469 , 470 ]).…”

“…medical waste, garbage, sludge) [ 447 ]; medical applications (np. sterilisation, drying, diagnosis, novel methods for treating inoperable tumours) [ 447 , 484 ]; analytical chemistry (laboratory sample processing, ashing, digestion, extraction, moisture analysis) [ 432 , 485 ]; chemical reactions: organic and inorganic synthesis (microwave assisted synthesis of e.g., medications, polymers and nanomaterials) [ 406 , 407 , 429 , 430 , 431 , 432 , 433 , 434 , 435 , 436 , 437 , 438 , 439 , 440 , 441 , 442 , 443 , 444 , 447 , 455 , 475 , 476 , 477 , 478 , 479 , 480 , 486 , 487 , 488 , 489 , 490 , 491 , 492 , 493 , 494 , 495 ]. …”