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Human beings are attempting to take advantage of renewable natural resources by using solar cells. These devices take the sun’s radiation and convert it into electrical energy. The issue with traditional silicon-based solar cells is their manufacturing costs and environmental problems. For this reason, alternatives have been developed within the solar cell field. One of these alternatives is the dye-sensitized solar cell (DSSC), also known as Grätzel solar cells. DSSCs are a type of solar cell that mimics photosynthesis. They have a photoanode, which is formed by a semiconductor film sensitized with a dye. Some of their advantages include low-cost manufacturing, eco-friendly materials use, and suitability for most environments. This review discusses four important aspects, with two related to the dye, which can be natural or synthetic. Herein, only natural dyes and their extraction methods were selected. On the other hand, this paper discusses the nanostructures used for DSSCs, the TiO2 nanostructure being the most reported; it recently reached an efficiency level of 10.3%. Finally, a review on the novelties in DSSCs technology is presented, where it is observed that the use of Catrin protein (cow brain) shows 1.45% of efficiency, which is significantly lower if compared to Ag nanoparticles doped with graphene that report 9.9% efficiency.

Adsorption stand out among other standard techniques used for water treatment because of its remarkable simplicity, easy operation, and high removal capability. Expanded graphite has been selected as a promising agent for oil spill adsorption, but its production involves the generation of corrosive remnants and massive amounts of contaminated washing waters. Although the advantageous use of the H2O2–H2SO4 mixture was described in 1978, reported works using this method are scarce. This work deals with the urgent necessity for the development of alternative chemical routes decreasing their environmental impact (based on green chemistry concepts), presenting a process for expanded graphite production using only two intercalation chemicals, reducing the consumption of sulfuric acid to only 10% and avoiding the use of strong oxidant salts (both environmentally detrimental). Three process parameters were evaluated: milling effect, peroxide concentration, and microwave expansion. Some remarkable results were obtained following this route: high specific volumes elevated oil adsorption rate exhibiting a high oil–water selectivity and rapid adsorption. Furthermore, the recycling capability was checked using up to six adsorption cycles. Results showed that milling time reduces the specimen’s expansion rate and oil adsorption capacity due to poor intercalant insertion and generation of small particle sizes.

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Calcium aluminate-based refractory ceramic was developed as an innovative refractory material, using garden snail (Helix aspersa) shells as a natural source of CaCO 3. A 1:1 molar ratio mixture of CaCO 3 from snail shells and commercial Al 2 O 3 powder was prepared by means of high-energy mechanical milling. The mixed powder was compacted in cylindrical samples (disks) and consolidated by sintering at 1450°C and 1500°C for 1h. The density and porosity were evaluated using the Archimedes principle, while the mechanical properties (hardness, fracture toughness, and shear modulus) were determined by indentation and ultrasonic methods, respectively. The thermal shock resistance was tested by heating samples to temperatures between 900 and 1400°C and subsequent quenching in water at room temperature. X-ray diffraction patterns of sintered samples indicate the formation of different calcium aluminate phases, such as CaAl 12 O 19 (krotite/monoclinic), CaAl 4 O 7 (grossite/monoclinic) and CaAl 2 O 4 (hibonite-5H/hexagonal). The fracture toughness and shear modulus values of materials sintered at 1450°C were higher (0.48 MPa•m 1/2 and 59 GPa, respectively) than those of materials sintered at 1500°C (0.43 MPa•m 1/2 and 55 GPa, respectively). Also changes in the bulk density, hardness and thermal shock resistance values were observed in materials sintered at 1450°C and 1500°C.