"Strength does not come from physical capacity. It comes from an indomitable will." - Mahatma Gandhi
PUBLISHED WORK
References and Links to Papers
November 2020
November 2018
The research investigates the efficiency of biochar to eliminate an emerging contaminant, flame retarding chemical, a.k.a. Tetrakis (Hydroxymethyl) Phosphonium Chloride (THPC) from water. The THPC, which is a water-soluble, organophosphorus salt, is mainly used by textile industries as a flame retardant and crease resistant for cotton and cellulose fabrics. Our research explores the possible removal process of THPC from water while using biochar as a mode of adsorption. Commercial biochar was used to investigate the adsorption efficiency of THPC. Spectroscopic and surface characterization data were provided for the commercial biochar. Study showed the presence of several organic functional groups on biochar which have potential to contribute to an efficient adsorption process. Batch adsorption studies were conducted varying several parameters like biochar dosages, contact time of the substrate to biochar, agitation time, and temperature during the experiment. It was found that benign experimental conditions such as lower biochar dosage, lower temperature and lower agitation time maximized the adsorption capacity. Furthermore, biochar was chemically treated with various activation agents and the removal efficiency was compared between activated and non-activated biochar. It was found that chemical activation on biochar indeed improved the THPC removal efficiency. Results also indicates that the adsorption mechanism of THPC on to biochar surface followed both Langmuir and Freundlich isotherms. Finally, it was observed that the adsorption process was fitted best with pseudo-second-order kinetic model which might indicate a possible chemisorption mechanism for the adsorption of THPC on biochar surface.
SYNTHESIS, CHARACTERIZATION, COMPUTATIONAL STUDY, AND BIOLOGICAL RELEVANCE OF A FAMILY OF ISOSTRUCTURAL, MONONUCLEAR LN (LN = GD, TB, DY, HO, ER) COMPLEXES CONTAINING PYRIDOXINE, AN ESSENTIAL INGREDIENT OF VITAMIN B6 ENZYME
August 2017
The synthesis and characterization of a family of LnIII complexes (Ln = Gd(1), Tb(2), Dy(3), Ho(4) and Er(5)) of formula [(LnIII(NO3)2(OH2)(pyridoxine)2](NO3) are reported, where pyridoxine is 2-methyl-3-hydroxy-4,5-bis(hydroxymethyl)pyridine. They were obtained from the reaction of Ln(NO3)3 with pyridoxine in ethanol in a 1:1 M ratio. The crystal structures of representative 1 and 5 were obtained using a single-crystal X-ray diffractometer. The subsequent characterization of all the complexes was performed using elemental analysis, IR spectroscopy and UV–Vis spectroscopy. The gadolinium complex was further analyzed to determine if DNA is a biological target of this series of metal complexes. In this regard, the interaction between the gadolinium complex and DNA was probed utilizing circular dichroism spectroscopy. The study supports the moderate binding of complex 1 to DNA.
January 2021
Our work in the area of synthesis of polynuclear manganese complexes and their
magnetic properties led to the synthesis and crystallization of the title
compound, [Mn₇(C₈H₉NO₃)₄(C₈H₁₀NO₃)₄(C₂H₅O)₂(C₇H₅O₂)₂O₂] 8C₂H₅OH.
Herein, we report the molecular and crystal structure of the title compound, which was
synthesized by the reaction of Mn(C₆H₅COO)₂ with pyridoxine (PNH₂, C₈H₁₁NO₃) followed
by the addition of tetramethylammonium hydroxide (TMAOH). The core of this
centrosymmetric complex is a cage- like structure consisting of six MnIII ions and one
MnII ion bound together through Mn—O bonds. The compound crystallizes in hydrogen-bonded layers
formed by O—H N hydrogen bonds involving the aromatic amine group of the ligand PN² with
the neighboring O atoms from the PNH ligand. The crystal structure has large voids
present in which highly disordered solvent molecules (ethanol) sit. A solvent mask was
calculated and 181 electrons were
found in a volume of 843 A˚ 3 in one void per triclinic unit cell. This is consistent
with the presence of seven ethanol molecules per formula unit, which accounts for 182 electrons per
unit cell. Additionally, one ethanol molecule was found to
be ordered in the crystal.
September 2011
The synthesis and characterization of a family of Mn2IIIMn2IILnIII2 complexes (Ln = Gd (1), Tb (2), Dy (3), and Ho (4)) of formula [Mn4Ln2O2(O2CBut)6(edteH2)2(NO3)2] are reported, where edteH4 is N,N,N′,N′-tetrakis(2-hydroxyethyl)ethylenediamine. The analogous Mn4Y2 (5) complex has also been prepared. They were obtained from reaction of Ln(NO3)3 or Y(NO3)3 with Mn(O2CBut)2, edteH4, and NEt3 in a 2:3:1:2 molar ratio. The crystal structures of representative 1 and 2 were obtained, and their core consists of a face-fused double-cubane [Mn4Ln2(μ4-O2–)2(μ3-OR)4] unit. Such double-cubane units are extremely rare in 3d metal chemistry and unprecedented in 3d–4f chemistry. Variable-temperature, solid-state dc and ac magnetic susceptibility studies on 1–5 were carried out. Fitting of dc χMT vs T data for 5 gave Jbb (MnIII···MnIII) = –32.6(9) cm–1, Jwb (MnII···MnIII) = +0.5(2) cm–1, and g = 1.96(1), indicating a |n, 0, n⟩ (n = 0–5) 6-fold-degenerate ground state. The data for 1 indicate an S = 12 ground state, confirmed by fitting of magnetization data, which gave S = 12, D = 0.00(1) cm–1, and g = 1.93(1) (D is the axial zero-field splitting parameter). This ground state identifies the MnII···GdIII interactions to be ferromagnetic. The ac susceptibility data independently confirmed the conclusions about 1 and 5 and revealed that 2 displays slow relaxation of the magnetization vector for the Mn4Tb2 analogue 2. The latter was confirmed as a single-molecule magnet by observation of hysteresis below 0.9 K in magnetization vs dc field scans on a single crystal of 2·MeCN on a micro-SQUID apparatus. The hysteresis loops also displayed well-resolved quantum tunneling of magnetization steps, only the second 3d–4f SMM to do so.
November 2011
The syntheses, crystal structures, and magnetochemical characterization are reported for the new mixed-valent Mn clusters [Mn2IIMnIII(O2CMe)2(edteH2)2](ClO4) (1), [MnII2MnIII2(edteH2)2(hmp)2Cl2](MnIICl4) (2), [MnIII6O2(O2CBut)6(edteH)2(N3)2] (3), [Na2MnIII8MnII2O4(OMe)2(O2CEt)6(edte)2(N3)6] (4), and (NEt4)2[Mn8IIIMn2IIO4(OH)2-(O2CEt)6(edte)2(N3)6](5), where edteH4 is N,N,N′,N′-tetrakis-(2-hydroxyethyl)ethylenediamine and hmpH is 2-(hydroxymethyl)pyridine. 1–5 resulted from a systematic exploration of the effect of different Mn sources, carboxylates, the presence of azide, and other conditions, on the Mn/edteH4 reaction system. The core of 1 consists of a linear MnIIMnIIIMnII unit, whereas that of 2 is a planar Mn4 rhombus within a [MnII2MnIII2(μ3-OR)2] incomplete-dicubane unit. The core of 3 comprises a central [MnIII4(OR)2] incomplete-dicubane on either side of which is edge-fused a triangular [MnIII3(μ3-O)] unit. The cores of 4 and 5 are similar and consist of a central [MnII2MnIII2(μ3-OR)2] incomplete-dicubane on either side of which is edge-fused a distorted [MnIIMnIII3(μ3-O)2(μ3-OR)2] cubane unit. Variable-temperature, solid-state direct current (dc) and alternating current (ac) magnetization studies were carried out on 1–5 in the 5.0–300 K range, and they established the complexes to have ground state spin values of S = 3 for 1, S = 9 for 2, and S = 4 for 3. The study of 3 provided an interesting caveat of potential pitfalls from particularly low-lying excited states. For 4 and 5, the ground state is in the S = 0–4 range, but its identification is precluded by a high density of low-lying excited states.
March 2022
Water pollution is a growing environmental concern in southeastern Georgia. This environmental quality assessment study was conducted at the Georgia Southern University (GSU) campus in Statesboro, Georgia with the objectives of analyzing the surface water quality for common urban contaminants and identifying their sources. The campus was divided into five zones (North, East-Central, East, West-Central, and South-West) and water was collected monthly from 50 different sites (ponds, drainage ditches, creeks) for a 10-month period during the 2014–2015 school year. Twelve contaminants, including six inorganic anions (bromide, chloride, fluoride, nitrate, phosphate, and sulfate) and six metal cations (boron, copper, iron, magnesium, potassium, and zinc) were tested using ion chromatography (IC) and inductively coupled plasma-mass spectrometry (ICP-MS). The contaminant levels in the water were compared to the US Environmental Protection Agency (USEPA) and the World Health Organization (WHO) standard guidelines for water quality assessment. Results showed that the mean campus contaminant levels of eleven out of twelve contaminants were well within the regulated limits, which indicate a healthy aquatic environmental quality at the GSU Statesboro campus. The aquatic concentrations for most of the contaminants varied significantly among different parts of the campus. The South-West zone and East zone showed the highest and lowest contaminant levels, respectively. The agricultural chemicals (fertilizers, herbicides, pesticides) used on campus for landscape management were identified as key sources of pollution followed by the discharges from campus automobiles (motor oil, brake lining, tire wearing), and recycled waterlines. Contaminant concentrations also varied seasonally, with summer months and January being higher and mid-late spring being lower. The seasonal variation was influenced by the rainfall pattern, chemical application timing, and algal growth. The findings of this study will also be helpful for future surface water pollution studies, especially in managed urban landscapes.
October 2015
Three new ruthenium alkylidene complexes (PCy3)Cl2(H2ITap)Ru=CHSPh (9), (DMAP)2Cl2(H2ITap)Ru=CHPh (11) and (DMAP)2Cl2(H2ITap)Ru=CHSPh (12) have been synthesized bearing the pH-responsive H2ITap ligand (H2ITap = 1,3-bis(2’,6’-dimethyl-4’-dimethylaminophenyl)-4,5-dihydroimidazol-2-ylidene). Catalysts 11 and 12 are additionally ligated by two pH-responsive DMAP ligands. The crystal structure was solved for complex 12 by X-ray diffraction. In organic, neutral solution, the catalysts are capable of performing standard ring-opening metathesis polymerization (ROMP) and ring closing metathesis (RCM) reactions with standard substrates. The ROMP with complex 11 is accelerated in the presence of two equiv of H3PO4, but is reduced as soon as the acid amount increased. The metathesis of phenylthiomethylidene catalysts 9 and 12 is sluggish at room temperature, but their ROMP can be dramatically accelerated at 60 °C. Complexes 11 and 12 are soluble in aqueous acid. They display the ability to perform RCM of diallylmalonic acid (DAMA), however, their conversions are very low amounting only to few turnovers before decomposition. However, both catalysts exhibit outstanding performance in the ROMP of dicyclopentadiene (DCPD) and mixtures of DCPD with cyclooctene (COE) in acidic aqueous microemulsion. With loadings as low as 180 ppm, the catalysts afforded mostly quantitative conversions of these monomers while maintaining the size and shape of the droplets throughout the polymerization process. Furthermore, the coagulate content for all experiments stayed <2%. This represents an unprecedented efficiency in emulsion ROMP based on hydrophilic ruthenium alkylidene complexes.
ENGAGING UNDERGRADUATE STUDENTS IN AUTHENTIC RESEARCH IN THE INORGANIC CHEMISTRY LABORATORY COURSE
2021
Book chapter published at Engaged Student Learning: Essays on Best Practices in the University System of Georgia
Jan 2021
The overall goal of this research was to study the effects of temperature and pine-to-HDPE ratios on the pyrolysis products. Catalytic co-pyrolysis of pine and HDPE was carried out in a double-column staged reactor, wherein the temperature was varied as 450 °C, 500 °C, and 550 °C for each pine/HDPE ratio of 0/100, 25/75, 50/50, 75/25, and 100/0. Thermal cracking of the feedstock is initiated at the first column, and the zeolitic-based ZSM-5 catalyst offered secondary cracking at a catalyst-to-feedstock ratio of 1:1 in the second column of the reactor. Catalytic pyrolysis of HDPE produced 31 wt% pyrolysis oil (40 MJ/kg calorific value) with a selectivity of above 90% toward gasoline-range hydrocarbons at 500 °C. Comparatively, pine offered 26.3% wt.% pyrolysis liquid yield with 7.9% dark pyrolysis oil (30 MJ/kg calorific value) that has a gasoline selectivity of 69.3%. Thus, the addition of HDPE increased the gasoline selectivity by increasing the hydrogen/carbon effective (H/Ceff) ratio. At pine/HDPE ratio of 25/75, the pyrolysis oil content was 22.5% at 500 °C, which is 3 times more than that of pine pyrolysis. The optimum yield and higher gasoline selectivity were observed at 500 °C for 0/100 and 25/75 pine to HDPE ratios
SYNTHESIS AND CHARACTERIZATION OF TWO NEW MIXED-VALENT MN6 COMPLEXES DERIVED FROM A WELL-EXPLORED 2‑HYDROXYMETHYL PYRIDINE ALONG WITH THE USE OF NEWLY EMPLOYED CARBOXYLATE IONS
November 2018
The syntheses, crystal structures and magnetochemical characterization are reported for two new mixed-valent manganese complexes, [MnII2MnIII2(H2O)2(hmp)6(NO3)2][MnII(NO3)3hmpH]2 (1) and, [MnII2MnIII4O2(hmp)4(hmpH)2(EtC(Me)2COO)4Cl2](EtC(Me)2COO)2 (2) incorporating the anion of 2‑hydroxymethyl pyridine. Complexes were further characterized by elemental analysis, IR & UV–Visible spectroscopy, single-crystal X-ray diffraction and thermogravimetric analysis. Variable temperature, solid-state direct current (dc) magnetization studies were carried out on both the complexes 1 and 2 in the 5.0–310 K range, and they established the complexes to have ground state spin values of S = 9 for 1 and S = 4 for 2.