Thios does the same as yoiur code, using a loop, and a simplified plot call:
x = 0:1:100;
Co = 22;
t1 = 30000;
t2 = 60000;
t3 = 120000;
t = [t1 t2 t3];
D = 0.001;
for k = 1:numel(t)
C(k,:) = Co*erf(x/(D*t(k)).^0.5);
end
figure
plot(x,C)
grid
It is may be a bit more efficient. I did not assess that specifically.
