Two laboratory tests were carried out to verify the suitability of an Italian commercial biochar as an adsorbing material. The chosen contaminant, considered dissolved in groundwater, was As. The circular economic concept demands the use of such waste material. Its use has been studied in recent years on several contaminants. The possibility of using an efficient material at low cost could help the use of low-impact technologies like permeable reactive barriers (PRBs). A numerical model was used to derive the kinetic constant for two of the most used isotherms. The results are aligned with others derived from the literature, but they also indicate that the use of a large amount of biochar does not improve the efficiency of the removal. The particular origin of the biochar, together with its grain size, causes a decrease in contact time required for the adsorption. Furthermore, it is possible that a strong local decrease in the hydraulic conductibility does not allow for a correct dispersion of the flow, thereby limiting its efficiency.

https://www.mdpi.com/2073-4441/13/7/915/pdf

Experimental and numerical study of biochar fixed bed column for the adsorption of arsenic from aqueous solutions

In the current review of the journal Structural Chemistry, the content of the issues 4–6 for the calendar year 2011 is related to thermochemistry. To the summary of each paper, a brief thermochemical commentary is added.

Interplay of thermochemistry and Structural Chemistry, the journal (volume 22, 2011, issues 4–6) and the discipline

The selective control of O–H/O–D bond dissociation in reduced dimensionality model of HOD molecule has been explored through IR+UV femtosecond pulses. The IR pulse has been optimized using simulated annealing stochastic approach to maximize population of a desired low quanta vibrational state. Since those vibrational wavefunctions of the ground electronic states are preferentially localized either along the O–H or O–D mode, the femtosecond UV pulse is used only to transfer vibrationally excited molecule to the repulsive upper surface to cleave specific bond, O–H or O–D. While transferring from the ground electronic state to the repulsive one, the optimization of the UV pulse is not necessarily required except specific case. The results so obtained are analyzed with respect to time integrated flux along with contours of time evolution of probability density on excited potential energy surface. After preferential excitation from |0, 0⟩ (|m, n⟩ stands for the state having m and n quanta of excitations in O–H and O–D mode, respectively) vibrational level of the ground electronic state to its specific low quanta vibrational state (|1, 0⟩ or |0, 1⟩ or |2, 0⟩ or |0, 2⟩) by using optimized IR pulse, the dissociation of O–D or O–H bond through the excited potential energy surface by UV laser pulse appears quite high namely, 88% (O–H ; |1, 0⟩) or 58% (O–D ; |0, 1⟩) or 85% (O–H ; |2, 0⟩) or 59% (O–D ; |0, 2⟩). Such selectivity of the bond breaking by UV pulse (if required, optimized) together with optimized IR one is encouraging compared to the normal pulses.

Selective bond breaking mediated by state specific vibrational excitation in model HOD molecule through optimized femtosecond IR pulse: A simulated annealing based approach

A comparative study on full diagonalization of Hessian matrix and Gradient-only technique to trace out reaction path in doped noble gas clusters using stochastic optimization

In this communication we would like to explore the idea of obtaining structures and IR spectral features of I2−(H2O)n cluster with n = 2 to 6. The approach taken up by us is a two tire one with initial good quality pre-optimized structures being found out by exploring a suitably constructed empirical potential energy surface and using the stochastic optimizer simulated annealing to explore the surface. These structures are then further refined using quantum chemical calculation to obtain the final structure and the IR spectra. We clearly show that the initial pre-optimization can indeed pave the way for quick and better convergence on subsequent quantum chemical refinement. To give credence to our effort we have also shown the evolutionary trend in vertical detachment energy (VDE) as a function of cluster size.

Structural and spectroscopic studies of iodine dimer radical anion hydrated clusters: an approach using a combination of stochastic and quantum chemical methods

In this article, we explore the use of stochastic optimization technique, namely simulated annealing, in elucidating the correct cut-off limit for suppression of Coulomb explosion in dicationic argon gas clusters. We also do a detail study of cluster sizes where the clusters are not stable as one single entity, and try to find out the dissociation channels for these, namely fission or non-fission type. We compare our results with available literature results, both theoretical and experimental.

Study of coulomb explosion and dissociation channels in dicationic argon clusters: a study based on stochastic optimization

In this paper, we explore the use of stochastic optimizer, namely simulated annealing (SA) followed by density function theory (DFT)-based strategy for evaluating the structure and infrared spectroscopy of (H2O)
 n
 OH− clusters where n = 1–6. We have shown that the use of SA can generate both global and local structures of these cluster systems. We also perform a DFT calculation, using the optimized coordinate obtained from SA as input and extract the IR spectra of these systems. Finally, we compare our results with available theoretical and experimental data. There is a close correspondence between the computed frequencies from our theoretical study and available experimental data. To further aid in understanding the details of the hydrogen bonds formed, we performed atoms in molecules calculation on all the global minimum structures to evaluate relevant electron densities and critical points.

/pdf/study-of-structure-and-spectroscopy-of-water-hydroxide-ion-1cfzuugsg5.pdf

Study of structure and spectroscopy of water–hydroxide ion clusters: A combined simulated annealing and DFT-based approach

In this paper we explore the possibility of using stochastic optimizers, namely Simulated Annealing (SA) in locating critical points (global minima, local minima, and first order saddle points) in argon noble gas clusters. The atomic interaction potential is the Lennard–Jones potential. We also try to see if a continuous transformation in geometry during the search process can lead to a realization of a kind of minimum energy path (MEP) for transformation from one minimum geometry to another through a transition state (first order saddle point). We try our recipe for three sizes of argon cluster, namely ( Ar ) 8 , ( Ar ) 10 and ( Ar ) 12 .

Satyajit Guha

Papers

Study of coulomb explosion and dissociation channels in dicationic argon clusters: a study based on stochastic optimization

Study of structure and spectroscopy of water–hydroxide ion clusters: A combined simulated annealing and DFT-based approach

Locating critical points and constructing reaction paths in noble gas clusters: A simulated annealing based study