Considering you have not trained for 6 months, and you state you've lost "practically all your muscle", I think you should consider yourself a beginner again. There are many workout plans out there suitable for beginners. The ones that work well are those which keep certain aspects of the novice trainee in mind:
- A focus on strength development, which will have the greatest potential during the novice phase.
- Training each muscle group every 48 to 72 hours, since for novices this is sufficient time to recover from each training.
- Linear progression for the weight lifted.
rrirower commented that there is no perfect plan since much depends on individuality. This is true, but tuning a plan requires plenty of experience with one's own strengths and weaknesses, with training in general, and a knowledge of the theory behind programming. Instead of doing some homebrew program without really knowing if it would benefit you, it would be better to go with one of the beginner programs that are highly popular, because they tend to be so for a reason. Good choices for 3 workouts per week would be Starting Strength, or StrongLifts 5x5. A good choice for 4 workouts per week that I have (positive) experience with is Johnny Candito's linear program. There are 3 variations for a focus on form, explosive power or hypertrophy.
Some problems I see with your program is only training your lower body once per week, which neglects a lot of development potential. In the worst case this infrequent stimulus would not be sufficient to drive the adaptation needed for linear progression. In the best case it's a lot slower than it could be. Also, as Noshii mentioned, triceps might be better to combine with chest and biceps with back, since you tend to use triceps on chest exercises (like the bench press) and biceps on back exercises (like rows and pull-ups). It's also more convenient from a warm-up perspective. However, if at least 48 hours are allowed for recovery between workouts you could mix it up the way you did.
Rather than take a wild guess at what might be optimal, rely on the experience of professionals out there and follow a well-designed program for novices. You'll find a large set of reviews for programs in this link: http://www.powerliftingtowin.com/powerlifting-programs/ This is with regard to how well they would benefit a powerlifter, but you should find some useful information regardless of your goals. If multiple programs seem suitable and you're wondering which one to choose, go for practical considerations: does it look like you would enjoy the exercises, does the program's layout appeal to you and is it feasible for you to follow it? For example, if you don't care that much about explosive power because you don't need it for some particular sport, and your gym is highly unsuitable for olympic lifts, maybe avoid programs involving them.