Graphene Prepared via the Dry Ice in Flames Method and its Purification Using Different Routes: A Comparative Study

Although the dry ice method used to synthesize exfoliated graphite/graphene is little known and used, it has significant advantages over others: it is low cost, simple, and a large quantity of material can be obtained using some inorganic and highly available acids (which can be reused). Despite the above advantages, the main reason for its incipient development is the resulting presence of magnesium oxide in the final product. In the present work, three different treat-ments were tested to remove this remnant using some acid chemical leaching processes, making use of hydrochloric acid, aqua regia, and piranha solution. Based on the experimental evidence, it was found that using aqua regia and combining the leaching process with mechanical milling was the most efficient way of removing such a remnant, the residue being only 0.9 wt.%. This value is low when compared to that obtained with the other acid leaching solutions and purifi-cation process (2.8 - 29.6 wt.%). A mandatory high-energy mechanical milling stage was neces-sary during this treatment, in order to expose and dissolve the highly insoluble oxide without secondary chemical reactions on the graphenes. High-energy mechanical milling is an effective route to exfoliate graphite/graphene, which allows the magnesium oxide to be more susceptible to acid treatment. The obtained surface area was 504 m2g-1; this high value resulting from the in-tense exfoliation can potentiate the use of this material for a wide variety of applications.

Effects of leachates from UV-weathered microplastic on the microalgae Scenedesmus vacuolatus

Plastics undergo successive fragmentation and chemical leaching steps in the environment due to weathering processes such as photo-oxidation. Here, we report the effects of leachates from UV-irradiated microplastics towards the chlorophyte Scenedesmus vacuolatus. The microplastics tested were derived from an additive-containing electronic waste (EW) and a computer keyboard (KB) as well as commercial virgin polymers with low additive content, including polyethylene (PE), polyethylene terephthalate (PET), polypropylene (PP), and polystyrene (PS). Whereas leachates from additive-containing EW and KB induced severe effects, the leachates from virgin PET, PP, and PS did not show substantial adverse effects in our autotrophic test system. Leachates from PE reduced algae biomass, cell growth, and photosynthetic activity. Experimental data were consistent with predicted effect concentrations based on the ionization-corrected liposome/water distribution ratios (Dlip/w) of polymer degradation products of PE (mono- and dicarboxylic acids), indicating that leachates from weathering PE were mainly baseline toxic. This study provides insight into algae toxicity elicited by leachates from UV-weathered microplastics of different origin, complementing the current particle- vs. chemical-focused research towards the toxicity of plastics and their leachates. Graphical abstract

Graphene Prepared via the Dry Ice in Flames Method and Its Purification Using Different Routes: A Comparative Study

Although the dry ice method used to synthesize exfoliated graphite/graphene is little known and used, it has significant advantages over others: it is low cost, simple, and a large quantity of material can be obtained using some inorganic and highly available acids (which can be reused). Despite the above advantages, the main reason for its incipient development is the resulting presence of magnesium oxide in the final product. In the present work, three different treatments were tested to remove this remnant using some acid chemical leaching processes. Based on the experimental evidence, it was found that using aqua regia, among other chemical mixtures, was the most efficient way of removing such as remnant, the residue being only 0.9 wt.%. A mandatory high-energy mechanical milling stage was necessary during this treatment, in order to expose and dissolve the highly insoluble oxide without secondary chemical reactions on the graphenes. The obtained surface area was 504 m2g-1; this high value resulted from the intense exfoliation can potentiate the use of this material for a wide variety of applications.

Clay Minerals Effects for Metal Reclamation from Leached Solution

The recent advancements in technology play a pivotal role in mankind’s life and have a significant stint in the generation of E-waste. The present investigation focuses on the recovery of heavy metals from Printed Circuit boards (PCBs) by applying two efficient techniques viz., leaching and adsorption. A combination of leaching and adsorption is a novel and productive approach to recovering heavy metals from like PCBs. After the phases of chemical leaching, the solution was recovered through adsorption and is eco-friendly. The process is carried out to increase the separation rate, reduce the time spent and reach the limits of incineration and pyrolysis methods. Adsorption provides the recovery of heavy metals with respect to the required adsorbent since it is a surface phenomenon. The optimum condition of process variables was found through response surface methodology (RSM). The maximum recovery of copper ions (97.33%) was obtained at the optimum operating conditions such as adsorbent size of 0.04 mm, adsorbent dosage of 3.5 gm L−1 and the temperature of 80°C with 0.845 desirability. This investigation was found to be an eco-friendly way to recover copper ions and does not cause any environmental issues.

Assessment of Groundwater Quality beneath Agriculturally Advanced Region of Northern Alluvial Plain, India

In the present study, groundwater suitability for domestic and irrigation purposes was analyzed in the alluvial aquifers of the Bist-Doab region of Punjab, India, using various indices such as WQI, WAWQI, MCDA, RSC, SAR, PI, %Na, KR, MH, PS, K, and Ka. Since it is difficult to assess the suitability of groundwater for irrigation based on various indices individually, a composite groundwater quality index for irrigation (CGQII) was used in the study which transforms nine indices to a single value for each sample. Results reveal that the groundwater of a few blocks was found unsuitable for domestic use due to chemical leaching from fertilizers, pesticides, and agricultural and industrial wastes. Whereas, the groundwater of mainly southwestern parts was found unsuitable for irrigation due to long-term water accumulation in aquifers and continuous use of sodium-ion-rich groundwater. The findings conclude that anthropogenic activities have played a significant role in making groundwater unfit for domestic and irrigation purposes in the study area. The present study also emphasizes continuous monitoring and evaluation of groundwater quality, which will help in strategic planning and management for the conservation of groundwater resources in the region.

CHEMICAL LEACHING OF CONTAMINATED SOIL – CASE STUDY

This study presents results of chemical leaching of contaminated soil from several metallurgically loaded locality of Richnava in Slovakia, applying two chelants – Na2EDTA and Na3EDDS of different molar concentration, done at different leaching conditions. The lower molar concentration (2 mM) of chelants showed comparable effect on Mn, Ni, As, Sb and Co leaching. Higher extraction was revealed at application of 10 mM chelants, especially for Cu and Cd release. Repeated washing of soil by 10 mM chelant without the media regeneration was more effective at the toxic elements removal than washing by smaller volumes of media or leaching of soil in static conditions. Final experiments focused on obtained leachates treatment showed that electrolysis and precipitation should represent a perspective way of the washing media regeneration.