Sonication cải thiện phản ứng Fenton

Fenton reactions are based on the generation of free radicals such as hydroxyl •OH radical and hydrogen peroxide (H₂O₂). The Fenton reaction can be significantly intensified when combined with ultrasonication. The simple, but highly efficacious combination of Fenton reaction with power ultrasound has been shown to drastically improve the desired radical formation and thereby process intensifying effects.

How Does Power Ultrasound Improve Fenton Reactions?

When high-power / high-performance ultrasonication is coupled into liquids such as water, the phenomenon of acoustic cavitation can be observed. In the cavitational hot-spot, minute vacuum bubbles arise, and grow over several high-pressure / low-pressure cycles caused by the power ultrasound waves. At the point, when the vacuum bubble cannot absorb more energy, the void collapses violently during a high-pressure (compression) cycle. This bubble implosion generates extraordinarily extreme conditions where temperatures as high as 5000 K, pressures as high as 100 MPa, and very high temperature and pressure differentials occur. The bursting cavitation bubbles also generate high-speed liquid microjets with very intense shear forces (sonomechanical effects) as well as free radical species such as OH radicals due to hydrolysis of water (sonochemical effect). The sonochemical effect of free radical formation are the major contributor for ultrasonically intensified Fenton reactions, whilst the sonomechanical effects of agitation improve mass transfer, which improves chemical conversion rates.
(The picture left shows acoustic cavitation generated at the sonotrode of the ultrasonicator UIP1000hd. Red light from the bottom is used for improved visibility)

Exemplary Case Studies for Sonchemically Enhanced Fenton Reactions

The positive effects of power ultrasound on Fenton reactions has been widely studied in research, pilot and industrial settings for various applications such as chemical degradation, decontamination and decomposition. The Fenton and sono-Fenton reaction is based on the hydrogen peroxide decomposition using an iron catalyst, which results in the formation of highly reactive hydroxyl radicals.
Free radicals such as hydroxyl (•OH) radicals are often purposely generated in processes to intensify oxidation reactions, e.g., to degrade pollutants such as organic compounds in wastewater. Since power ultrasound is an auxiliary source of free radical formation in Fenton type reactions, sonication in combination with Fenton reactions enhanced pollutant degradation rates in order to degrade pollutants, hazardous compounds as well as cellulose materials. This means that an ultrasonically intensified Fenton reaction, the so-called sono-Fenton reaction, can improve the hydroxyl radical production making the Fenton reaction significantly more efficient.

Sonocatalytic–Fenton Reaction for Enhances OH Radical Generation

Ninomiya et al. (2013) demonstrate successfully that a sonocatalytically enhanced Fenton reaction – using ultrasonication in combination with titanium dioxide (TiO2) as catalyst – exhibits a significantly enhanced hydroxyl (•OH) radical generation. The application of high-performance ultrasound allowed to initiate an advanced oxidation process (AOP). Whilst sonocatalytic reaction using TiO2 particles have been applied to the degradation of various chemicals, the research team of Ninomiya used the efficiently generated •OH radicals to degrade lignin (a complex organic polymer in cell walls of plant) as a pretreatment of lignocellulosic material for a facilitated subsequent enzymatic hydrolysis.
The results show that a sonocatalytic Fenton reaction using TiO2 as sonocatalyst,enhances not only the degradation of lignin but also is an efficient pretreatment of lignocellulosic biomass in order to enhance the subsequent enzymatic saccharification.
Procedure: For the sonocatalytic–Fenton reaction, both TiO2 particles (2 g/L) and Fenton reagent (i.e., H2O2 (100 mM) and FeSO4·7H2O (1 mM)) were added to the sample solution or suspension. For the sonocatalytic–Fenton reaction, the sample suspension in the reaction vessel was sonicated for 180 min with the probe-type ultrasonic processor UP200S (200W, 24kHz) with sonotrode S14 at an ultrasound power of 35 W. The reaction vessel was placed in a water bath maintaining a temperature 25°C using a cooling circulator. The ultrasonication was performed in the dark in order to avoid any light-induced effects.
Effect: This synergistic enhancement of OH radical generation during the sonocatalytic Fenton reaction is attributed to the Fe3+ formed by Fenton reaction being regenerated to Fe2+ induced by the reaction coupling with the sonocatalytic reaction.
Kết quả: Đối với phản ứng Fenton xúc tác sono, nồng độ DHBA được tăng cường hiệp đồng lên 378 μM, trong khi phản ứng Fenton không cần siêu âm và TiO2 chỉ đạt được nồng độ DHBA là 115 μM. Sự thoái hóa lignin của sinh khối kenaf dưới phản ứng Fenton chỉ đạt được tỷ lệ thoái hóa lignin, tăng tuyến tính lên đến 120 phút với kD = 0,26 phút−1, đạt 49,9% sau 180 phút; trong khi với phản ứng sonocatalytic-Fenton, tỷ lệ thoái hóa lignin tăng tuyến tính lên đến 60 phút với kD = 0,57 min−1, đạt 60,0% sau 180 phút.

Scanning electron micrographs (SEM) of kenaf biomass (A) untreated control, pretreated with (B) sonocatalytic (US/TiO2), (C) Fenton (H2O2/Fe2+), and (D) sonocatalytic–Fenton (US/TiO2 + H2O2/Fe2+) reactions. Pretreatment time was 360 min. Bars represent 10 μm.
(Picture and study: ©Ninomiya et al., 2013)

Naphtalene Degradation via Sonochemical Fenton

tỷ lệ phân hủy naphthalene cao nhất đạt được ở giao điểm của nồng độ hydro peroxide cao nhất (600 mg L-1) và thấp nhất (nồng độ naphthalene 200 mg kg1) của cả hai yếu tố cho tất cả các cường độ chiếu xạ siêu âm được áp dụng. Nó dẫn đến 78%, 94% và 97% hiệu quả thoái hóa naphthalene khi sonication ở 100, 200 và 400 W, tương ứng, được áp dụng. Trong nghiên cứu so sánh của họ, các nhà nghiên cứu đã sử dụng máy siêu âm Hielscher UP100H, UP200Stvà UP400ST. Sự gia tăng đáng kể về hiệu quả suy thoái là do sự hiệp đồng của cả hai nguồn oxy hóa (siêu âm và hydro peroxide) được dịch thành diện tích bề mặt tăng của oxit Fe bằng siêu âm ứng dụng và sản xuất các gốc hiệu quả hơn. Các giá trị tối ưu (600 mg L−1 hydro peroxide và 200 mg kg1 nồng độ naphthalene ở 200 và 400 W) cho thấy giảm tối đa 97% nồng độ naphthalene trong đất sau 2 giờ xử lý.
(cf. Virkutyte et al., 2009)

SEM–EDS microgram of a) elemental mapping and b) soil prior and c) after ultrasound irradiation treatment
(Picture and study: ©Virkutyte et al., 2009)

Sonochemical Carbon Disulfide Degradation

Adewuyi and Appaw demonstrated the successful oxidation of carbon disulfide (CS2) of in a sonochemical batch reactor under sonication at a frequency of 20 kHz and 20°C. The removal of CS2 from the aqueous solution significantly increased with an increase in ultrasound intensity. Higher intensity resulted in an increase in the acoustic amplitude, which results in an intenser cavitation. The sonochemical oxidation of CS2 to sulfate proceeds mainly through oxidation by the •OH radical and H2O2 produced from its recombination reactions. In addition, the low EA values (lower than 42 kJ/mol) in both the low- and high-temperature range in this study suggest that diffusion-controlled transport processes dictate the overall reaction. During ultrasonic cavitation, the decomposition of water vapour present in the cavities to produce H• and •OH radicals during the compression phase has been already well studied. The •OH radical is a powerful and efficient chemical oxidant in both the gas and liquid phase, and its reactions with inorganic and organic substrates are often near the diffusion-controlled rate. The sonolysis of water to produce H2O2 and hydrogen gas via hydroxyl radicals and hydrogen atoms is well-known and occurs in the presence of any gas, O2, or pure gases (e.g., Ar). The results suggest that the availability and the relative rates of diffusion of free radicals (e.g., •OH) to the interfacial reaction zone determine the rate-limiting step and the overall order of the reaction. Overall, sonochemical enhanced oxidative degradation is an effective method for carbon disulfide removal.
(Adewuyi and Appaw, 2002)

Ultrasonic Fenton-like Dye Degradation

The effluents from industries that use dyes in their production are an environmental problem, which is requires an efficient process in order to remediate the waste water. Oxidative Fenton reactions are widely used for treating dye effluents, whilst improved Sono-Fenton processes are getting increasingly attention due to its enhanced efficiency and its environmental-friendliness.

Sono-Fenton Reaction for Degradation of Reactive Red 120 Dye

Sự xuống cấp của thuốc nhuộm Reactive Red 120 (RR-120) trong nước tổng hợp đã được nghiên cứu. Hai quá trình đã được xem xét: Sono-Fenton đồng nhất với sắt (II) sulfate và Sono-Fenton không đồng nhất với goethite tổng hợp và goethite lắng đọng trên cát silica và canxit (chất xúc tác biến đổi GS (goethite lắng đọng trên cát silica) và GC (goethite lắng đọng trên cát canxit), tương ứng). Trong 60 phút phản ứng, quy trình Sono-Fenton đồng nhất cho phép suy thoái 98,10%, trái ngược với 96,07% đối với quy trình Sono-Fenton không đồng nhất với goethite ở pH 3,0. Việc loại bỏ RR-120 tăng lên khi các chất xúc tác biến đổi được sử dụng thay vì goethite trần. Các phép đo Nhu cầu oxy hóa học (COD) và Tổng lượng carbon hữu cơ (TOC) cho thấy việc loại bỏ TOC và COD cao nhất đã đạt được với quy trình Sono-Fenton đồng nhất. Các phép đo nhu cầu oxy sinh hóa (BOD) cho phép phát hiện ra rằng giá trị cao nhất của BOD / COD đã đạt được với quy trình Sono-Fenton không đồng nhất (0,88±0,04 với chất xúc tác biến đổi GC), chứng minh rằng khả năng phân hủy sinh học của các hợp chất hữu cơ còn lại đã được cải thiện đáng kể.
(cf. Garófalo-Villalta et al. 2020)
The picture left shows the ultrasonicator UP100H used in the experiments for red dye degradation via sono-Fenton reaction.(Study and picture: ©Garófalo-Villalta et al., 2020.)

Heterogeneous Sono-Fenton degradation of azo dye RO107

Jaafarzadeh et al. (2018) demonstrated the successful removal of azo dye Reactive Orange 107 (RO107) via sono-Fenton like degradation process using magnetite (Fe3O4) nanoparticles (MNP) as catalyst. In their study, they used the Hielscher UP400S ultrasonicator Được trang bị SONOTRODE 7mm ở chu kỳ làm việc 50% (1 giây bật / 1 giây tắt) để tạo ra sự xâm thực âm thanh để có được sự hình thành gốc mong muốn. Các hạt nano magnetit hoạt động như chất xúc tác giống như peroxidase, do đó sự gia tăng liều lượng chất xúc tác cung cấp các vị trí sắt hoạt động mạnh hơn, từ đó đẩy nhanh quá trình phân hủy H2O2 dẫn đến việc sản xuất OH • phản ứng.
Results: Complete removal of azo dye was obtained at 0.8 g/L MPNs, pH = 5, 10 mM H2O2 concentration, 300 W/L ultrasonic power and 25 min reaction time. This ultrasonic Sono-Fenton like reaction system was also evaluated for real textile wastewater. The results showed that chemical oxygen demand (COD) was reduced from 2360 mg/L to 489.5 mg/L during a 180 min reaction time. Moreover, cost analysis was also conducted on the US/Fe3O4/H2O2. Finally, ultrasonic/Fe3O4/H2O2 showed high efficiency in decolorization and treatment of coloured wastewater.
An increase in ultrasonic power led to an enhancement in reactivity and surface area of magnetite nanoparticles, which facilitated the transformation rate of `Fe3+ to `Fe2+. The as-generated `Fe2+ catalyzed a H2O2 reaction in order to produce hydroxyl radicals. As a result, the increase of ultrasonic power was shown to enhance the performance of US/MNPs/H2O2 process by accelerating the decolorization rate within a short period of contact time.
The authors of the study note that ultrasonic power is one of the most essential factors influencing on the degradation rate of RO107 dye in the heterogeneous Fenton-like system.
Learn more about highly efficient magnetite synthesis using sonication!
(cf. Jaafarzadeh et al., 2018)

RO107 degradation in different combinations at pH of 5, MNPs dosage of 0.8 g/L, H2O2 concentration of 10 mM, RO107 concentration of 50 mg/L, ultrasonic power of 300 W and reaction time of 30 min.
Study and picture: ©Jaafarzadeh et al., 2018.

ultrasonicators hạng nặng

Hielscher Ultrasonics designs, manufactures and distributes high-performance ultrasonic processors and reactors for heavy-duty applications such as advanced oxidative processes (AOP), Fenton reaction, as well as other sonochemical, sono-photo-chemical, and sono-electro-chemical reactions. Ultrasonicators, ultrasonic probes (sonotrodes), flow cells and reactors are available at any size – from compact laboratory test equipment to large-scale sonochemical reactors. Hielscher ultrasonicators are available a numerous power classes from laboratory and bench-top devices to industrial systems capable to process several tons per hour.

Precise Amplitude Control

The amplitude is one of the most important process parameter influencing the results of any ultrasonic process. Precise adjustment of the ultrasonic amplitude allows to operate Hielscher ultrasonicators at low to very high amplitudes and to fine-tune the amplitude exactly to the required ultrasonic process conditions of applications such as dispersion, extraction and sonochemistry.
Choosing the right sonotrode size and using optionally a booster horn for and additional increase or decrease of the amplitude allows to setup an ideal ultrasonic system for a specific application. Using a probe / sonotrode with a larger front surface area will dissipate the ultrasonic energy over a large area and a lower amplitude, whilst a sonotrode with smaller front surface area can create higher amplitudes creating a more focused cavitational hot spot.

Hielscher Ultrasonics manufactures high-performance ultrasonic systems of very high robustness and capable to deliver intense ultrasound waves in heavy-duty applications under demanding conditions. All ultrasonic processors are built to deliver full power in 24/7 operation. Special sonotrodes allow for sonication processes in high-temperature environments.

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