Nabil, M.A. Bahnasawy

Soil Chem. and Phys. Dep., DRC, Egypt

Key Words:kaolinite, bentonite, humic acid, fulvic acid, IR and active groups

ABSTRACT

The present study aims toassessment of organo- clay complex behavior using infrared (IR) technique. The results showed that the kaolinite clay mineral saturated with organic acids (humic and fulvic acids), Ca, Mg and Na cations, after the IR examination; the dominant active groups were: OH, N-H, C-H₂, C=O, C=C, Al-O, Si-OH, C-C, Al-OH and C-H and the wavenumber were (3500-3670), (3400-3445), (2900-3000), (1620-1660), 1610, 1350, 1080, (950-1070), 850 and 810 cm^-1 respectively.

Also the results  showed that the bentonite clay mineral impregnated with the same treatments and after examined by IR radiation that the active groups were:  OH, N-H, C=O, C=C, C-H, Si-O, C-C and Al-OH-Al and the wavenumber were (3250-3632), 3300, (950-1634), (1525-1631), (830-1068), (1048-1068), 1070 and (915-918) cm^-1 respectively.

At the least, the arrangements of active groups on kaolinite mineral were as follows: OH > CH > Al-OH = C=O> N-H = C-C = CH₂>C=C = Al-O = Si-OH. While the arrangements of active groups on bentonite mineral were as follows: OH > C=O = C=C>NH = CH>Si-O>Al-OH-Al>C-C.

INTRODUCTION

The organic complexes of clay play an effective role in determining the characteristics of physical and chemical of soil and its relationship to plant nutrition, therefore their study is important to determines the impact of these characteristics and their roles in improving soil properties (FAO, 2000). The present study clearly demonstrates that FT-IR spectroscopy is an efficient method for the characterisation of the purified bentonite in an organic mixture. This is technique remains economical, rapid, and specific (Eisazadeh, et al. 2012) .Therefore, the identification of the adhesion of clay minerals to the predominant organic acids (humic and fulvic) and the difference between them increases the importance of these acids in influencing soil properties and the binding of the necessary cations (Balcke, et al. 2002).

Using infrared radiation is leach to reach the most suitable installation that improves soil properties and their agricultural development potentials(Balcke, et al. 2002). The chemical structure of humic and fulvic acids are shown in Fig. (1).

 (Humic acid)                                                        (Fulvic acid)

         mical formula C₁₈₇H₁₈₆O₈₉N₉S₁                      Chemical formula C₁₃₅H₁₈₂O₉₅N₅S₂

(Sam Boggs, et al. 1985).

Fig. (1) Chemical structure of humic and fulvic acids

Humic substances are considered as the most important constituents of soils (Sara et al. 2010). They form the largest fraction of soil organic matter and play the dominant role in improving soil productivity (Jayaganesh and Senthurpandian, 2010). Humic substances are formed by the decomposition of plant and animal residues by microorganisms (Rao et al. 2019). Organic matter is intrinsic essential components of all soils (FAO 2017). The humic and fulvic substances play an important role in increasing productivity and soil fertility (Khan et al. 2018).

The plant growth, improvement of tuber nutritive value and quality and improvement in tuber size and weight in potato plants co-inoculated with Bacillus strains and humic acid, a significant improvement was observed in potato production. Despite a low total tuber yield (28.3 t ha^-1) in control treatment, combined inoculation increased potato production by around 140% which was with in the high range of the increase expected for both Bacillus strains and humic acid mono treatments. The stability and increased consistency of the potato plant response to bacterial inoculation in the presence of humic acid indicated a promising biotechnological tool to improve growth and adaptation of potatoes to field conditions  Ekin, (2019).

The present review was aimed to the technical procedural methods used by FT-IR for clay surface characterization because, FT-IR remain is an economical, rapid and common technique. A spectrum can be obtained in a few minutes and the instruments are sufficiently inexpensive as to be available in many laboratories according to Djomgoue and Njopwouo (2013).

Although there are different studies on the clay and organic matter complexes, they did not address the effective role of both fulvic and humic alone and their association with the cation structure on the surface of pure clay minerals to guide the importance of the type of clay minerals and their reciprocal cations in the reclaimed soil.

MATERIALS AND METHODS

Homoionic Clays

      Kaolinite and bentonite clays were purchased from Sigma-Aldrich Comp. Each of 10 g of clays was saturated with, Ca²⁺, Mg²⁺,and Na⁺ by five repeated treatments with 50 ml of 1M concentration of metal chloride. The cation-exchanged clays were thoroughly washed with water, and centrifuged for 10 min at 5000 rpm. The washing and centrifugation procedures were repeated until chloride ion was no longer detected by the AgNO₃ test by FAO, (2008).

Extraction of humic and fulvic substances

Humic (HA) and fulvic (FA) acids were extracted from sheep manure according to the standard method described by Sánchez-Monedero et al. (2002). The manure was mixed with deionized water at a rate of 1:5 (w/v) and then treated with 0.5 N NaOH solution to extract the humic substances. Humic acid was separated from humus extract by acidification with 0.1 M HCl to reach a pH of 2.0, after being left over-night. The precipitate was collected and the supernatant was again adjusted to pH between 4.5 and 5 using NaOH solution. The fulvic acid fraction got was settled after 24 h. Both the humic substances and fulvic acid fractions were washed with distilled water to remove impurities. Finally, black coloured fine crystals of humic acid and brown coloured crystals of fulvic acid fractions were obtained.

Organo clay complex will prepared by using two homoiconic clay for kaolinite and bentonite with (Ca, Mg, and Na) separately with humic and fulvic acids. Organic clay complex were prepared at ratio 1:100 following the procedure of Li et al., (2003) and Wang and Xing (2005). In brief, 0.5 g of HA and  FA were dissolved in a minimum volume of 0.5 M NaOH separately and stand overnight then up to 1000 ml to obtain final concentration, 500 mgl ^-1. The organic clay complex suspensions were intermittent shaking for one week. The sedimented particles were washed repeatedly with distilled water until no color, was seem in the supernatant. The washed organic clay complex was dried at 40 ^ᴼC, grounded and finally, passed through (170) mesh and sealed in the glass tube for use.

Infrared spectroscopy

The analysis of the infrared absorption of the pure clay minerals and  organic clay complex was carried out in KBr pellets using  Jasco FTIR-4100 from wavenumber 4000 to 400 cm^-1 (Ma, et al. 2010).

RESULTS AND DISCUSSIONS

Infrared spectra of humic and fulvic acids are shown in Fig. (2) and Table (1). Humic acid show broad absorption centered around at 3360, 1406, 1233 and 1060 cm^-1 regions (Edward et al., 2014). The phenolic (OH), amide, methyl, free-NH-bond, carboxylic and carbonyl group are presented in the humic and fulvic acids (Sharmah and Bordoloi, 1993). The absorption are around 1715 cm^-1 region and due to the C=O stretching, (Haworth, 1971). The absorption are around 1630 cm^-1 region that due to the C=C stretching vibrations of double bonds (Dorado et al., 2010). The 1200 cm^-1 band is assigned to C-O stretching of phenols, carboxylic acids, ethers and OH- deformation of –COOH (Stevenson, 1994). The relative intensity of major IR absorption bands of humic and fulvic acids are shown in Table (1).

              (Humic acid)                                        (Fulvic acid)    

Fig. (2) Infrared spectra of humic and fulvic acids

Table (1): Relative intensity of major IR absorption bands of humic and   fulvic acids

 Jayaganesh and Senthurpandian (2010)

Kaolinite mineral

Figs. (3 and 4) and Table (2) shows that Kaolinite Clay- organic complexes can be attributed to kaolinite by IR absorption spectra. Their IR spectra demonstrate fully-represented and well-resolved OH, Al-O and Al-OH bands of the mineral lattice around 3650, 1350 and 850 cm^-1 respectively. Kaolinite-Mg clearly-seen absorption bands of OH, Si-OH and Al-OH around 3500, 1080 and 850 cm^-1 respectively. As the infrared absorption spectra showed, the kaolinite mineral adsorbed with humic acid is that the active groups are O-H stretching (H bonded OH group), N-H stretching, C-H₂ stretching, C=O stretching of amide group and CH out of plane bending around wavenumber 3400, 2900, 1660 and 810 cm^-1 respectively.  As for the kaolinite-humic-Mg, the dominant active groups were: OH, CH₂ , C=C aromatic stretching and /or asymmetric –COO stretching, C-C stretching of aliphatic groups, C-O stretching of polysaccharides or polysaccharide-like, CH out of plane bending around the wavenumber  3680, 3000, 1620, 1070, 950, 810 and 775 cm^-1 respectively.

Fig. (3): Infrared spectra of Kaolinite Clay-Organic Complexes

Fig.(4) Kaolinite structure, showing the interlayer hydrogen bonds (Blanca, 2015)

Table (2): Infrared spectra of Kaolinite clay–Organic complexes

*W.N= wavenumber

Bentonite mineral

Figs. (5 and 6) and Table (3) shows that bentonite clay- organic complexes can be attributed to bentonite by IR absorption spectra. Their IR spectra demonstrate fully-represented and well-resolved OH stretching, H-bending OH, free OH, intermolecular bonded OH, C=O, Si-O stretching and Al-OH-Al bending   bands around wavenumber 3632, 3422, 1634, 1048 and 918  cm^-1 respectively. Bentonite-Mg clearly-seen absorption bands of OH, C=O, Si-O stretching, Al-OH-Mg bending and Si-O stretching around 3250, 1634, 1048, 843 and 778 cm^-1 respectfully. As the infrared absorption spectra showed, the bentonite mineral adsorbed with humic acid (bentonite-humic) that the active groups were N-H stretching, C=C aromatic stretching and /or asymmetric –COO stretching,-CH- polysaccharides, C=O stretching and CH out of plane around wavenumber 3300, 1600, 1050, 950 and 775 cm^-1 respectively.  As for the bentonite-humic-Mg, the dominant active groups were: OH,  stretching, N-H stretching, C=C aromatic stretching and /or asymmetric –COO stretching, C-C stretching of aliphatic groups, C-O stretching of polysaccharides or polysaccharide-like, CH out of plane bending around the wavenumber  3600, 3300, 1620, 1070, 950, and 830 cm^-1 respectively.

 However bentonite mineral saturated with fulvic acid and sodium cation (bentonite-fulvic-Na) the effective groups were  OH stretching, N-H stretching, C=C aromatic stretching, Si-O stretching, Al-OH-Al bending and Al-OH- around 3632, 3300, 1525, 1068, 915 and 842 cm^-1 respectively. While bentonite saturated with fulvic acid and calcium cation (bentonite-fulvic- Ca) the active groups were OH stretching, C=C aromatic stretching and, CH out of plane around 3632, 1620, and 830 cm^-1 respectively. At least, bentonite mineral saturated with fulvic acid and magnesium cation (bentonite-fulvic-Mg) indicated the effective groups were H-bonded OH, free OH, N-H stretching, C=C aromatic stretching, CH stretching, C=O stretching of polysaccharides or polysaccharide –like substances and CH out of plane around wavenumber 3400, 3300, 1631, 1068, 950 and 775 cm^-1 respectively. 

Fig.(5): Infrared spectra of Bentonite clay-organic complexes

Fig. (6) Bentonite structure, showing the interlayer hydrogen bonds (Jun, et al. 2019).

Table (3): Infrared spectra of Bentonite clay –Organic complexes

*W.N= wavenumber