The primary, most obvious parameter indicating water quality is the color of the water. Not only can it be aesthetically disturbing, but it can also be an indicator of contamination. Clean, high-quality water is a valuable, essential asset. Of the available technologies for removing dyes, adsorption is the most used method due to its ease of use, cost-effectiveness, and high efficiency. The adsorption process is influenced by several parameters, which are the basis of all laboratories researching the optimum conditions. The main objective of this review is to provide up-to-date information on the most studied influencing factors. The effects of initial dye concentration, pH, adsorbent dosage, particle size and temperature are illustrated through examples from the last five years (2017–2021) of research. Moreover, general trends are drawn based on these findings. The removal time ranged from 5 min to 36 h (E = 100% was achieved within 5–60 min). In addition, nearly 80% efficiency can be achieved with just 0.05 g of adsorbent. It is important to reduce adsorbent particle size (with Φ decrease E = 8–99%). Among the dyes analyzed in this paper, Methylene Blue, Congo Red, Malachite Green, Crystal Violet were the most frequently studied. Our conclusions are based on previously published literature.

Based on the well-known excellent adsorbent ability of chicken eggshells, the adsorptive capacity and mechanism of Remazol Brilliant Violet-5R (RBV-5R) dye by eggshell was investigated. Exploiting the high surface-area-to-volume ratio and porous structure of this natural adsorbent, the developed procedure showed to be useful for the efficient adsorption of RBV-5R dye from contaminated water. The protocol was thoroughly optimized by investigating the effect of the dye concentration, biomass-contaminated water ratio, particle size of the adsorbent, pH and temperature, as they are key factors in the efficiency of the dye removal process. The eggshell material was characterized by different types of microscopy techniques (stereo, polarization, SEM) as well as elemental analysis (element distribution mapping, EDX), Raman spectroscopy and BET-surface density measurements. EDX, FTIR and Raman spectroscopy proved the presence of the adsorbed dye on the surface of the biomaterial. It was shown that under optimal conditions, the environmentally friendly and inexpensive eggshell could be a reliable adsorbent for Remazol dye removal from wastewater.

Organic pollutants, such as dyes, have a negative effect on the aqueous environment, therefore, their elimination from water bodies is a high priority. In this work, Eichhornia crassipes and Salvinia natans, both model plants with high phytoremediation efficiency, were exposed to various concentrations (C_i = 50–500 mg/L) of Eriochrome Black T (EBT). Their capacity to assimilate EBT was studied for 16 days of exposure, similar to natural conditions and by spectrophotometric monitoring of the dye concentration (E_{E. crassipes; 150 mg/L} = 33%; E_{S. natans; 150 mg/L} = 71.5%). The changes of the experimental parameters (pH—equalised by day 5, temperature, humidity, light intensity) were followed, and plant growth and biochemical responses to toxic stress effects (photosynthetic pigments, Energy-dispersive X-ray spectroscopy (EDX)—decreased effect of P, Mg, Ca, S and K, Scanning electron microscopy (SEM), defense enzyme) were examined. Furthermore, changes in oxidative- and photo-degradation of EBT in time and the solid-state properties (SEM, EDX, Fourier-transform infrared spectroscopy-FTIR) of the dye were investigated. Our results demonstrate that, despite the toxic stress, both species succeeded in reducing the dye-concentration of the water and S. natans proved to be more efficient in binding and removing organic dyes. With our findings, we proved that both plants alleviated the abiotic stress of dye contamination.

The aim of this study is to investigate and develop a phytoremediation method for the removal of two triphenylmethane dyes (crystal violet and malachite green) using an aquatic plant, Lemna minor. The effects of operational parameters such as aquatic plant quantity, initial dye concentration, initial pH of the solutions and temperature of the medium were studied in order to determine the optimum phytoremediation conditions. The plant’s photosynthetic pigments were determined quantitatively in order to detect the plant’s response to abiotic stress. During the phytoremediation experiments the parallel sub-processes (phytosorption, phytoextraction, phytodegradation) were observed and analysed. The mechanisms of phytoremediation were studied using Fourier transformation infrared spectroscopy, ultraviolet-visible spectroscopy, thin layer chromatography and Energy-dispersive X-ray spectroscopy. Results show that the plant tolerated high concentrations (300 mg/L) of dyes, and was able to remove from the environment and accumulate in its cells the dyes up to a significant percentage (crystal violet was removed by about 80% and malachite green by 90%).

The excellent adsorption properties of clay minerals make the optimization of heavy metal removal the subject of numerous research projects. In the present study, ASLAVITAL cosmetic clay (ACC) powder was applied for the removal of Cd²⁺ from water. The main deposit of ACC clay is the Pădurea Craiului Mountains in Romania. A wide range of morpho-structural approaches (SEM, EDX, FTIR, Raman, XRD) were used to characterize the morphology and elemental composition of the adsorbent. As expected for clay minerals, Al (Wt(%) = 11.4 ± 0.9) and Si (Wt(%) = 13.7 ± 1.4) are the main constituents of ACC. After adsorption, Wt(%) = 0.2 ± 0.01 Cd²⁺ was detected in the sample. As proved before, the initial metal concentration is the primary influencing factor; therefore, batch adsorption of 10–160 mg/L Cd²⁺ was investigated. After 190 min, an efficiency of 99% was reached, and the quantity in equilibrium increased from 1–8 mg/g. The best fit in linear form was obtained for the Langmuir II. model, where R² = 0.954 (R_L = 0.037–0.027). Based on linear isotherm models, physical bonds formed between ACC and Cd²⁺ during the favorable adsorption. For the non-linear fits, the Liu model proved to be the best R² = 0.965, χ² = 1.101. Pseudo-II-order kinetic model described the experimental data R² = 0.988–0.999; q_exp and q_calc were almost identical (the differences ranged 0.03–0.34).

As a result of climate change, drought and heat significantly reduced plant growth. Therefore, this study aims to explore and provide more insight into the effect of different arbuscular mycorrhizal fungi (AMF) strains (Rhizophagus irregularis, Funneliformis mosseae, and Funneliformis coronatum) on tomato plant tolerance against combined drought and heat stress, as well as combined drought and heat shock. A pot experiment was performed under controlled conditions in a growth chamber at 26/20 °C with a 16/8 h photoperiod. After six weeks of growth, one-third of plants were put in non-stress conditions, while another one-third were subjected to combined drought and heat stress (40% field capacity for two weeks and 38 °C/16 h and 30 °C/8 h for 5 days). The rest of the plants were exposed to combined drought and heat shock (40% of field capacity for two weeks and 45 °C for 6 h at the end of the drought period). All data were evaluated by one- and two-way analysis of variance (ANOVA). Means were compared by Duncan’s post hoc test at p < 0.05. The obtained results showed that combined drought and heat stresses had no significant impact on root colonization. Furthermore, stressed AMF plants exhibited a decrease in hydrogen peroxide and malondialdehyde content in the cells and showed changes in defense enzyme activities (peroxidase (POD), catalase (CAT), polyphenol oxidase (PPO), and glutathione S-transferase (GST)) in leaves as well as in roots compared with their relative non-mycorrhizal plants.