João P. Vareda

Bio: João P. Vareda is an academic researcher from University of Coimbra. The author has contributed to research in topics: Adsorption & Aerogel. The author has an hindex of 11, co-authored 16 publications receiving 476 citations.

Effect of different silylation agents on the properties of ambient pressure dried and supercritically dried vinyl-modified silica aerogels

Abstract: Despite their unique properties, pure silica aerogels usually exhibit a few applications on a large-scale due to their hydrophilic behavior and brittleness. To overcome these drawbacks, hydrophobic, fiber-reinforced tetraethoxysilane/vinyltrimethoxysilane (TEOS/VTMS) derived aerogels were synthesized and dried at ambient pressure and under supercritical conditions for comparison. The silylation of the silica surface is crucial prior to ambient pressure drying (APD) and is favored by the already existing vinyl groups in the silica skeleton. In this work, the influence of different silylating agents on the final properties of the aerogels was studied, varying the number of methyl groups of the agent. With the increase of methyl groups in the agent and/or its reactivity, the decrease of shrinkage by APD is more pronounced, reaching values similar to the supercritically dried counterparts. The thermal insulation performance, hydrophobicity and flexibility improve in the same trend.

Heavy metal water pollution: A fresh look about hazards, novel and conventional remediation methods

Abstract: Water pollution is one of the global challenges that society must address in the 21st century aiming to improve water quality and reduce human and ecosystem health impacts. Industrialization, climate change, and expansion of urban areas produce a variety of water pollutants. In this work, we discuss some of the most recent and relevant findings related to the release of heavy metals, the possible risks for the environment and human health, the materials and technologies available for their removal. Anthropogenic activities are identified as the main source of the increasing amounts of heavy metals found in aquatic environments. Some of the health hazards derived from repeated exposure to traces of heavy metals, including lead, cadmium, mercury, and arsenic, are outlined. We also give some perspectives about several techniques used to detect heavy metals, as well as about the factors that could affect the contaminant removal. The advantages and drawbacks of conventional and non-conventional heavy metal removal methods are critically discussed, given particular attention to those related to adsorption, nanostructured materials and plant-mediated remediation. Some of the commercial products currently used to eliminate heavy metals from water are also listed. Finally, we point out some the requirements and opportunities linked to developing efficient methods for heavy metal removal, such as the ones that exploit nanotechnologies.

Cellulose Aerogels: Synthesis, Applications, and Prospects.

Abstract: Due to its excellent performance, aerogel is considered to be an especially promising new material. Cellulose is a renewable and biodegradable natural polymer. Aerogel prepared using cellulose has the renewability, biocompatibility, and biodegradability of cellulose, while also having other advantages, such as low density, high porosity, and a large specific surface area. Thus, it can be applied for many purposes in the areas of adsorption and oil/water separation, thermal insulation, and biomedical applications, as well as many other fields. There are three types of cellulose aerogels: natural cellulose aerogels (nanocellulose aerogels and bacterial cellulose aerogels), regenerated cellulose aerogels, and aerogels made from cellulose derivatives. In this paper, more than 200 articles were reviewed to summarize the properties of these three types of cellulose aerogels, as well as the technologies used in their preparation, such as the sol–gel process and gel drying. In addition, the applications of different types of cellulose aerogels were also introduced.

“Traditional” Sol-Gel Chemistry as a Powerful Tool for the Preparation of Supported Metal and Metal Oxide Catalysts

Abstract: The sol-gel method is an attractive synthetic approach in the design of advanced catalytic formulations that are based on metal and metal oxide with high degree of structural and compositional homogeneity. Nowadays, though it originated with the hydrolysis and condensation of metal alkoxides, sol-gel chemistry gathers plenty of fascinating strategies to prepare materials from solution state precursors. Low temperature chemistry, reproducibility, and high surface to volume ratios of obtained products are features that add merit to this technology. The development of different and fascinating procedure was fostered by the availability of new molecular precursors, chelating agents and templates, with the great advantage of tailoring the physico-chemical properties of the materials through the manipulation of the synthesis conditions. The aim of this review is to present an overview of the “traditional” sol-gel synthesis of tailored and multifunctional inorganic materials and their application in the main domain of heterogeneous catalysis. One of the main achievements is to stress the versatility of sol-gel preparation by highlighting its advantage over other preparation methods through some specific examples of the synthesis of catalysts.