Toxicity Effects of Microplastics and Nanoplastics with Cadmium on the Alga Microcystis Aeruginosa

The objective of this paper is to present a thorough analysis of the toxicity of microplastics (MPs) and nanoplastics (NPs) with the heavy metal cadmium (Cd). These components were studied separately and combined to determine how these environmental toxins affect Microcystis aeruginosa (M. aeruginosa) in fresh water. The combined toxicity of MPs or NPs and Cd to M. aeruginosa showed an aggressive and negative effect after 96 h of exposure. Due to the higher adsorption ability of NPs, the accumulation of Cd inside cells with NPs was lower than that found inside the cells with MPs. But the difference in toxicity between the MPs and NPs was not significant. Meanwhile, the more produce of the extracellular polymeric substance (EPS) in the presence of NPs, the more complex effect of EPS bonded to heavy metals, which reduce the toxic effect on the algal cells. Notably, the production of microcystin-LR (MC-LR) under different treatments has demonstrated that the presence of combined MPs/NPs with Cd can potentially raise some of the toxin risks harming the aquatic environment. Our findings highlight the great potential ecological risks of the combined Cd and MPs/NPs in the aquatic system.

Recent advances in the temporal and spatiotemporal dynamics induced by bromate–sulfite-based pH-oscillators

The bromate–sulfite reaction-based pH-oscillators represent one of the most useful subgroup among the chemical oscillators. They provide strong H+-pulses which can generate temporal oscillations in other systems coupled to them and they show wide variety of spatiotemporal dynamics when they are carried out in different gel reactors. Some examples are discussed. When pH-dependent chemical and physical processes are linked to a bromate–sulfite-based oscillator, rhythmic changes can appear in the concentration of some cations and anions, in the distribution of the species in a pH-sensitive stepwise complex formation, in the oxidation number of the central cation in a chelate complex, in the volume or the desorption-adsorption ability of a piece of gel. These reactions are quite suitable for generating spatiotemporal patterns in open reactors. Many reaction–diffusion phenomena, moving and stationary patterns, have been recently observed experimentally using different reactor configurations, which allow exploring the effect of different initial and boundary conditions. Here, we summarize the most relevant aspects of these experimental and numerical studies on bromate–sulfite reaction-based reaction–diffusion systems.

Fe and Ag supported on activated carbon as an effective adsorbent for 2,4-dichlorophenoxylacetic acid treatment: a theoretical study

Extended tight-binding quantum chemical method (GFN2-xTB) was performed to investigate the adsorption of 2,4-dichlorophenoxylacetic acid (2,4-D) on activated carbon (AC) and AC modified by Fe or Ag (AC-M). Electronic properties of the studied systems were estimated via vertical ionisation potential, vertical electron affinity, and global electrophilicity index. Adsorption energy, population analysis, and geometrical parameters were calculated to clarify the adsorption ability of AC and AC-M. The results indicated that the introduction of metal atoms to AC substantially enhanced the adsorption ability for 2,4-D. The adsorption mechanism changed from physical adsorption (on AC) to chemisorption (on AC-M). The influence of different solvents (water, methanol, and acetonitrile) on the adsorption process was studied via an Analytical linearized Poisson-Boltzmann algorithm.

Adsorption-Oxidation Mechanism of δ-MnO2 to Remove Methylene Blue

The material, δ-MnO2, has exhibited superior performance on the removal of methylene blue (MB), but the process is significantly impacted by pH, and the impacting mechanism is still unclear. In this study, the effects of pH on the removal mechanism of MB using synthesized δ-MnO2 were investigated by distinguishing the adsorption and oxidation of MB by δ-MnO2 during the removal process in the dark. The results show that the total removal efficiency of MB by δ-MnO2 decreased significantly with an increase in the pH. MB could be removed by δ-MnO2 via an adsorption mechanism and oxidation mechanism, and the proportion of adsorptive removal and oxidative removal was different under different pH conditions. With an increase in the initial pH from 2.00 to 8.05, the redox potential of δ-MnO2 decreased, and its oxidation ability for the removal of MB also gradually decreased. In contrast, the surface negative charges of δ-MnO2 increased with an increase in the pH, and the adsorption ability towards positively charged MB also gradually increased. This indicates that the effects of pH on the removal of MB by δ-MnO2 are primarily dominated by its influence on the oxidation ability of δ-MnO2. In addition, it is further proved that the pH value has a significant effect on the oxidation and adsorption of MB on δ-MnO2. Moreover, the significant effects of pH on the oxidation of MB by δ-MnO2 are further demonstrated by observing the changes in Mn2+ and the UV-Vis spectra of intermediate products during the reaction, as well as the changes in the FTIR and XPS characterizations of δ-MnO2 after the reaction.

Single and Binary Adsorption Behaviour and Mechanisms of Cd2+, Cu2+ and Ni2+ onto Modified Biochar in Aqueous Solutions

The chitosan–EDTA modified magnetic biochar (E–CMBC) was successfully used as a novel adsorbent to remove heavy metals. The adsorption behaviour and mechanisms of E–CMBC to Cd2+, Cu2+ and Ni2+ were performed in single and binary system in aqueous solutions. In single–metal system, the adsorption process of Cd2+, Cu2+ and Ni2+ on E–CMBC fitted well with the Avrami fractional–order kinetics model and the Langmuir isotherm model. The measured maximum adsorption capacities were 61.08 mg g−1, 48.36 mg g−1 and 41.17 mg g−1 for Cd2+, Cu2+ and Ni2+, respectively. In binary–metal system, coexisting ions have obvious competitive adsorption behaviour on E–CMBC when the concentration of heavy meal beyond 20 mg L−1. The maximum adsorption capacities of the heavy metals were found to be lower than that in single–metal system. The order of the competitive adsorption ability was Cu2+ > Ni2+ > Cd2+. Interestingly, in Cd2+–Cu2+ system the earlier adsorbed Cd2+ could be completely replaced by Cu2+ from the solution. Different competitive adsorption ability of those heavy metal were due to the characteristics of heavy metal and resultant affinity of the adsorption sites on E–CMBC. The adsorption mechanism indicated that chemical adsorption played a dominating role. Therefore, E–CMBC could be a potential adsorbent for wastewater treatment.

Improved Adsorption Capacity of Nannochloropsis sp. through Modification with Cetyltrimethylammonium Bromide on the Removal of Methyl Orange in Solution

In this research, biomass modification of Nannochloropsis sp. with surfactant cetyltrimethylammonium bromide (CTAB) through a cation exchange reaction to produce adsorbent Nannochloropsis sp.-cetyltrimethylammonium bromide (AlgN-CTAB) has been carried out. Biomass modification of Nannochloropsis sp. by CTAB has been successfully carried out through confirmation from the analysis data produced by Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM-EDX). AlgN-CTAB adsorbent has been tested for its adsorption ability against anionic dye of methyl orange (MO) in solution by way of a sequence of experiments by the batch method. The optimum conditions for MO removal from the solution occurred at an adsorbent quantity of 0.1 g, pH of 5, and an interaction time of 60 min. MO adsorption kinetic data by AlgN and AlgN-CTAB tended to take the kinetic model of pseudo-second-order (PSO) with PSO rate constant ( k 2 ) values of 0.56 and 2.17 g mg-1 min-1, serially. The MO adsorption isotherm pattern by AlgN tends to take the Freundlich adsorption isotherm, whereas in AlgN-CTAB it follows the Langmuir and Dubinin-Radushkevich adsorption isotherms. The results of the adsorption-desorption of MO by AlgN-CTAB with 4 repetition cycles resulted in % removal of MO > 80 % . The AlgN-CTAB adsorbent can be used repeatedly and is very effective in absorbing MO in water.

Insights into the Simultaneous Sorption of Ciprofloxacin and Heavy Metals Using Functionalized Biochar

Biochar and chitosan are considered as green and cost-effective adsorbents for water purification; the combination of these two materials may lead to an improved adsorption capacity of the generated adsorbents. Most sorption studies have been focused on the ability to adsorb one contaminant or the same type of contaminants. Thus, this study aimed to produce chitosan-biochar beads (CH-BB) and test their efficiency in the simultaneous removal of a metal-complexing antibiotic, ciprofloxacin (CIP), and three metal(loid)s (As, Cd and Pb). Modification of raw pig manure biochar resulted in an increase in its adsorption capacity, except for Pb. The highest increment was observed for As (almost 6-fold) and the lowest was observed for CIP (1.1-fold). The adsorbent was able to simultaneously remove all targeted contaminants, individually and in the mixture. The adsorption capacity of CH-BB followed the order: Pb > Cd > >As > CIP. When Pb and As were present in the same mixture, their removal efficiency increased from 0.13 ± 0.01 to 0.26 ± 0.05 mg/g for As and from 0.75 ± 0.08 to 0.85 ± 0.02 mg/g for Pb due to their co-precipitation. The CIP–metal complexation probably resulted in a reduced adsorption ability for inorganics due to the decreased concentration of free ions. The presence of metals and metalloids led to alterations in CIP’s mobility.

ADSORPTION OF CEFIXIME TRIHYDRATE ONTO CHITOSAN 10B FROM AQUEOUS SOLUTION: KINETIC, EQUILIBRIUM AND THERMODYNAMIC STUDIES

An efficient and biodegradable adsorbent chitosan 10B was used to eliminate cefixime trihydrate from aqueous solution. The kinetic behavior of cefixime trihydrate adsorption onto chitosan 10B was studied in aqueous medium, from various operational aspects, such as contact time, solution pH, antibiotic concentrations, and temperatures. Cefixime adsorption onto chitosan 10B was confirmed by Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FE-SEM) and energy-dispersive X-ray spectroscopy (EDX). The antibiotic adsorption kinetics obeyed a pseudo-second-order model rather than pseudo-first-order and Elovich kinetic models. The best illustration of antibiotic adsorption equilibrium was made by the Langmuir model, with the highest adsorption ability qm: 37.04 μmol/g at 298 K. The activation energy (Ea) of the present adsorption system was computed to be 44.18 kJ/mol. The values of activation (ΔG‡, ΔH‡ and ΔS‡) and thermodynamic (ΔG, ΔH and ΔS) parameters confirmed that the cefixime trihydrate adsorption onto chitosan 10B in aqueous medium is an exothermic physisorption process. Cefixime desorption from antibiotic-loaded chitosan 10B was performed in 0.1 M NaOH solution and the recycled adsorbent was utilized for a second time without significant loss of its adsorption capacity.